I used to use the Ross Gibson engines but due to his passing they are no longer available.
Here's how I do it now.
I usually start with one of the Revell Door Slammer kits such as this:
I use the main chassis, the two front down bars that connect to the firewall, the Lenco transmission, the suspension, tires, steering rack and the bell housing. If I'm doing a Pontiac, Olds, Chevy or Ford engine I will use the engine block in the kit.
Most of the time I go for a Hemi Engine out of one of Revell's modern-ish top fuel dragsters or Funny cars. The entire engine will be used for my build but I make a few modifications to it. First off I use the intake from the pro sportsman kit. This puts the blower a little further up in the air and accurately represents what they are doing in pro-mod now. I then add a plate on top of the intake for the blower to sit on. You can see the modified intake in primer in this pic:
As for the blower, I take the standard blower out of the top fuel kit and lengthen it. It doesn't have to be pretty as the blower bag will cover it:
Most Pro mod motors use single spark plug heads. I'll occasionally use the T/F covers and run two magnetos. Magnetos are usually made from aluminum tubing and topped by a pair of pre-wired distributors from Morgan Automotive detail. Decals from Slixx make them look convincing:
Blower pulleys and belts come from Machined Aluminum Specialties. You can see them in the previous pic. Blower shafts are aluminum tube because they are stronger with the tension of the rubber belt.
The injector hats come from competition resin or you can make your own.
I usually use the fuel pump out of the top fuel kit. Headers are kit pieces or I make my own.
Final details come from the Detail Master Blower Scoop Hardware photo-etch set.
here's a finished engine:
If you have any further question feel free to ask.