OK, my knowledge of the RST engine specifically is limited, but some initial pointers:

Your fully built engine, What exactly is in it? Its unlikely to be forged pistons and steel rods at 113bhp? If it is, whats the compression ratio? you will almost certainly want new pistons.

Head porting again, at 113bhp i wouldnt expect it to be too extreme but its easy to go too big!

What spec is the camshaft? is it a pattern standard one to meet race regs, or a modified one for N/A use? The standard one might be ok, but it might have too much overlap leaving you needing a turbo compatible cam be it standard or piper etc.

personally Id be aiming at something like a GT series like you suggest, but you need to make sure its suitable for the pressure and flow it will see. If not you can go old school with the T3. Unless you go for something ridiculous it will boost fine.

standard route = tuning standard bits

reliable route, expecially is its in a different car, without the 80s management guff is any of the aftermarket ecu's, dta, emerald, mtech etc. These also give you the benefit of electronic boost control which given the nature of car might be useful!

Your dry sump should be fine, the turbo oil demand is very low. An oil cooler might be required though.

I have to ask though, why not sell off the CVH with its dyno chart and forged bottom end and use a zetec instead on TBs or a lower boost pressure. Apart from period authenticity there is nothing good about a CVH.

Nice car and an interesting project!