Another Mopar Off My Bucket List - Barracuda Fastback

Yeah, like a Keith Black Hemi isn't a lot of cash :D
You could get one of the last BMW M5 inline sixes. They have some pretty impressing numbers. Probably a lot of electronics to wrestle, though:
Engine designation S38B38:
3,795 cc (232 cu in)
340 hp (250 kW) @ 6900 rpm
400 N·m (295 lb·ft) @ 4750 rpm
Naturally aspirated, like a BMW is supposed to be.