LS engines are transplanted into classic cars for a multitude of reasons. For example, the overall cost savings of swapping an engine vs. rebuilding your old gear and the ease of finding replacement and performance parts. Those bonuses teamed with the long-term benefits – reliability and gas mileage – are hard to beat. There is one thing that a vehicle wouldn’t receive a LS for: curb appeal. Not without a little more work, anyway. Plastic wasn’t as big of a “thing” in the 50s and 60s, and when you pop the hood on a classic, the general audience expects to see something a bit more authentic. That’s why it was decided to give this modern LS1 truck engine’s aesthetics an overhaul to better match the original 390 that once lived in this 1961 Cadillac.

The basis of this article can be applied to any LS swapped classic car. Replacing the intake manifolds and relocating the coils are the keys to hiding the insipid modern look of the LS that disappoints curious eyes. To give my setup classic flair, we chose a single-plane Holley EFI manifold with matching fuel rails, a Holley EFI throttle body, and Holley’s SBC to LS valve cover adaptors mated to Cadillac 390 covers to simulate a carbureted engine.

The truck-sourced LS1 that is sitting in this 1961 Cadillac's engine bay is certainly up to the task of providing the power. But when it comes to looks? Well...it certainly does not look like 1961 under the hood, does it?

The project began with a quick disassembly. After disconnecting the fuel lines and electrical harness and then removing the ignition coils, valve covers and the LS intake manifold, test fitting began. The fancy finned Cadillac 390 valve covers didn’t match the bolt pattern of the Holley SBC valve cover adapter plates, but we anticipated that small speed bump. What we didn’t anticipate was the stock truck-style LS alternator colliding with the bulky valve covers, something that wouldn’t have been an issue if the LS had been manufactured for a car.

An emergency modification of the stock alternator bracket lowered the unit to the desired height and slightly pushed it outward for maximum clearance. A Ford 4G alternator was used for its compact size. If you prefer to give your engine a complete face lift, Holley’s front drive accessory system is where it’s at, especially if you are blessed with a truck LS equipped with that in-your-face alternator.

Bolting the Cadillac 390 valve covers to the Holley SBC adapters took minimum modification. Four perimeter tabs (two per side) welded to each valve cover adaptor line up to the 390 valve cover bolt holes. A 2-inch round hole was measured and cut to integrate a custom oil fill and engine vent tube on the valley pan because the classic Cadillac valve covers don’t have provisions for either. The 2-inch wide by 4-inch tall chrome-plated pipe is welded to a flange that’s bolted to the valley pan. This was topped off with a chrome breather cap which was later painted black to better blend with the valve cover color scheme. The valley cover was immediately reinstalled to prevent any nasties from landing inside the engine.

In order to move on with the reassembly, we could no longer procrastinate on the mess of wiring that was left after “phase one” of this LS swap. Extra time was spent re-routing the wires and wrapping them with braided wire loom and black cloth electrical tape, which looks presentable for now. The alternative is to purchase a new plug-and-play harness for your application.

On to the fun stuff – after the valve cover adapters were bolted to the engine block, the ignition system got an upgrade utilizing MSD Ignition coils and spark plug wires. The engine was dressed up with the Cadillac 390 valve covers once everything was plugged in.

The MSD ignition coils (826283) are nicely hidden under the Cadillac covers and are connected to the spark plugs via Holley EFI LS spark plug wires (561-111).

Next, the block was topped with Holley’s EFI intake manifold. Its single-plane design mimics the vintage look of an intake you’d see on an old carbureted-style motor. Matching Holley EFI fuel rails were installed before bolting the intake to the block. The stock LS injectors fit like a glove with the help of ICT injector adapters, which are made to adapt the LS1 fuel rails to the truck injectors. We chose the universal 1,000cfm Holley throttle body, which happens to somewhat resemble a carburetor, to install on top of the manifold. The fuel system is plumbed using a Holley EFI fuel pressure regulator and tied together with a slew of Earl’s Performance AN fittings and hose.

For the grand finale, the throttle cable was re-connected and a visual check was performed to make sure all electrical connections were re-connected. For those who are working with a factory GM wiring harness and ECU, the Holley EFI throttle body uses a Chrysler style idle air controller (IAC), so the connector will require re-pinning.

A vintage batwing-style air filter housing provides the finishing touch and helps to further hide the injector and throttle body wires from an overhead viewpoint. One last thing: Since a MAF sensor is no longer used, a custom tune on the ECU is necessary before hitting the road.

Granted, there are still a few details that are “off” if you compare a Cadillac 390 engine and the decorated LS side-by-side, but we no longer hesitate to pop the hood for passersby.

Sure, if you take a close look you'll see the EFI rails and other details that will let you know that this is certainly not the original Cadillac 390ci engine under the hood. But compared to our "before" shot, it's a great improvement!