There has been some talk about the M156, but TBH, there are enough electrical issues with the M113(K) to keep one busy, without thinking about ESI, Drive Authority, etc, to think about a newer platform. There are probably a couple dozen Crossfires with M113/M113K swaps, and they're all pretty nice. I saw someone is selling a roadster with a 5.4L M113 that dyno'd at 400whp for sale on FB for $16.2k. Not bad, considering. The 'K' engines are pricey, and if you read my journal, you'll see there is a lot to do, particularly with the radiator/fan package. You'll still need a transmission to hold up to it, and support pieces like fuel, hoses, etc to deal with it all. the M113K bolted right up to everything, and in of itself, required no fabrication. If you live in a cooler climate than me, you might get by with little to no fab work. the nice part about the M113K is hat you are right at your HP goal, out of the box, with no mods to the engine. Put a pulley and a few other goodies on it, and you are way past your 500hp number, with plenty of room to spare.