Anybody care to offer an opinion on safe max bhp for My96 STI RA, assuming correct fuelling, timing, charge temp and boost?

Ignoring gearbox/clutch issues.

In other words, at what point do you need to do engine internals?

I would say 350-400 BHP, with progressively more risk the higher you go.

Depends on what chance you are prepared to take.

If you saw an engine failure as an opportunity to rebuild stronger then go for 400 BHP. If that possibility scares you 350 BHP.

Just my 2p.