Glad everything is going well! Did you get on a rolling road to confirm your engine power in the end? Chris seems to think 300bhp is about the limit of the chassis but, like you, if I do an engine swap I will be going for considerably more..
Current pondering is maybe the VW R32 V6 with turbo/procharger, should be about 450bhp in a mild tune. I've come to the conclusion that converting to a transaxle and Audi V8 might be pushing it all a bit too far with new rear suspension required...