Patrick makes fenton headers for the gmc and there are other headers out there for that engine. It seems as if all the hard work has been done for you. Installing a gmc engine in a chevy usually includes relocating the radiator a little bit forward. The gmc is between 1 and 1 1/2 inches longer than the chevy. There are other performance products available for the gmc engines such as four barrel intakes, dual and tripple carb intakes, even a 5 two barrel intake.
The 270 is a bulletproof engine that will go a very long time. Factory specs rate it at 130 hp. With careful consideration, and standard hot rodding techniques, it would not be difficult to get 190 - 200 hp out of that engine!
The jimmy engines were looked at in the early 50s as an ideal hotrod engine. Many jimmy power cars were record holders on the 1/4 mile track, and on the salt flats. Cars powered by a built Jimmy engine would blow the Ferds off the line in the 1/5 and 1/4 mile tracks
