The current popular Automotive Conversion V8 engine these days is the Chevy LS-1(or C-5), LS-2, LS-6 from Camarros, Corvettes, GTOs etc... The relatively inexpensive 5.7Litre engines are often made into 383cid strokers as the Torque is more "usable" in aeroplanes than the actual Horsepower ratings. Here's George Morse working on my LS-1 that will propell my Prowler/Jag.
This LS-1 was rescued from a wrecking yard and then rebuilt and converted using one of George's custom PSRUs & Accessory cases. It will use AirFlowPerformance manual controlled aviation fuel injection units running a 3 bladed McCauley constant speed prop and a dual electronic distributor ignition system - no computer required! There are other PSRUs on the market, but most all of them use belt drives while the Morse PSRU uses GM Muncie transmission gears (much more reliable!). With use of a VORTEC supercharger to maintain Sea-Level atmospheric pressure, the engine should be able to maintain approx. 385hp & 440ft-lbs torque all the way up to 25,000' ! Eventually, we'll find out - but, since I don't plan on flying at 25K' often (due to Oxygen requirements) I may only try it a few times just to "prove" the engine combination.