As you have found out, checking piston-to-wall clearance with a feeler gauge can be tricky. Piston manufacturers give you a gauge point to set the cylinder wall clearance. This is where you would measure the piston with an outside micrometer. Early forged pistons used a gauge point perpendicular to the wristpin. Most current forged pistons use a gauge point at 1/2 inch up from the end of the piston skirt. You see differing locations to measure the piston because of the cam-ground piston skirt. (This grinding allows the piston to grow as it heats up and become round to match the cylinder bore.) This is why you always want to get the engine up to operating temperature before putting high load on the engine. The cam ground skirts give your engine quieter operation during cold starts. Finally, cast pistons like those you are using also have specific cam-ground skirts, but cast pistons don’t grow as much as forged alloy pistons, so you can run much tighter piston-to-wall clearances with cast pistons. The pistons you used should have had a sheet with them to spec out the specific clearance and where to measure the clearance. If you have between 0.002 and 0.003 inch of clearance with a feeler gauge you should be fine. This is as you slide the piston down the cylinder with the gauge between the bottom of the skirt, 90 degrees from the wristpin axis. You will check this clearance from the bottom of the piston, centered in the skirt. Slide the feeler gauge into the cylinder, then try to slide the piston into the bore. Start on the small side (0.0015 inch) and increase the gauge size until a good tension is on the piston to slide it into the bore.
Let’s get down to your final question. We’d use an Edelbrock Performer intake manifold PN 2101. This has two different-sized intake runners between the upper and lower planes, to help broaden the torque curve and gain area under the curve. This will help move your Imp. For a nice carburetor, go with an Edelbrock Thunder Series AVS 500-cfm carburetor PN 1801; it features Air Valve secondaries that deliver proper airflow to the engine based on demand. As the engine speed increases, the secondary air valve opens to increase the airflow potential. The benefit of this type of carburetor is that the engine is never over-carbureted throughout the engine rpm range. The PN 1801 comes equipped with an electric choke for easy cold start and performance.
Good luck with your project, your friend is one lucky dude!
I have an ’88 Monte Carlo SS with a 358 with a 700-R4. I just put it together, but now I want to go fuel-injected. What are the big differences between building an LS motor or buying an EFI carb replacement bolt-on kit? I read about the Holley Avenger EFI kit, and it seems like a good, easy-to-install product. However, given the price, I was thinking I could buy an LS1 with the transmission. Yes, it might be more work, but I am a mechanic in the Air Force and work on many different vehicles, so I’m up for the challenge. I’m ready to take the T-tops off and scream down the road again!