Renegade in Las Vegas makes full kits for the Suby stuff too. I have to admit, if you are looking for 300-ish HP then I would do a turbo'd Suby combo as it would be lighter weight and lower cg. Because, as you noted, the buggy guys have been using those engines for awhile, the adapters to mate up to Porsche boxes, or aftermarket transaxles that follow the Porsche pattern, are easy to get.
If you want 450 HP or more, then definitely go V8; less high-strung to make that kind of power. Handling and rigidity will become a serious issue tho' with stock 914 stuff and hence why my car ended up tube frame and dual A
Adapting late model 997 susp front and rear was another idea I had that likely would have worked well (easier as it keeps the strut front end). Even so, after a lot of tuning, if you watch my vids behind the wheel, I looked more like a NASCAR guy at 200mph than a Porsche guy at 130mph
While crazy fast, it was a handful to keep pointed forward at times.
Still, pucker factor and all, it is an absolute blast to have that kind of HP to weight ratio that can also make turns...