Engine Build advice- 300-350 fwhp 
Chaps, 
New to this forum and thought I'd start by initiating a discussion on the build of a decent-spec subaru motor for use in an alternative vehicle; in this case a classic VW beetle. 
So I'm searching for base engines, and plan on rebuilding from the crank up to a completely finished motor. The question is, what engine should I start with in order to achieve the ultimate goal of 300-350 flywheel Hp? 
I understand that the 93- STI motors are the units with fully forged bottom ends, and closed deck block, meaning they are more suitable for high power applications. But is this necessary? I've always been a bigger fan of displacement; would going EJ25 turbo be a better route? In which case, which engine should I look for? 
I'd like to avoid sleeving blocks and expensive engineering exercises; but am happy to port, modify and lighten where necessary. Are the stock forged pistons good enough? Should I be looking at later base engines? 
Finally, what spec would you look for externally? Turbo, injectors etc? I already have an ECU lined up and am happy to tune myself- I've a fair amount of experience on this.  
Cheers for the advice in advance. 
Steve