I understand your basic question. yet you would need to lay out your complete build and intention before any of us could give you solid data. (if we have it)
And as Joe said. the bottom ends on a TypeIV block are extremely strong. (Read: basically bullet proof)
From what I have gathered from others. Staying under a 96 bore is best with cast iron cylinders. Any bore larger than 96 starts to create sealing issues with the heads.
As the mating surface of the cylinder gets smaller and smaller as diameter increases.
The exception to this is to use L&N engineerings NICKIES Cylinders. These are made from Billet aluminum and you can go nuts with boost on these...$$$
The stock rods will work. But they are very heavy and the bolts will need to be changed to something stronger.
Like ARP 2000 SBC bolts or some variation on that theme.
I like your idea of aftermarket rods and pistons. That is a best case scenario.
Your cam choice will be interesting. As the stock cam is far from ideal for a turbo engine.
I have a suggestion for you. Shoot over to STF.
STF forums
Go to the TYPE-4-RUM area. Thats a great place to ask about your turbo build. Jonas Linder is way over 280HP with his. And a few other guys are over 300 HP with their setup. or you can read about 280HP NON turboed TypeIVs
It is one of the few places that speaks turbo type IV in the US. It is done all the time in Europe. Kinda hard to find here in the US.
Hopefully this will help....
Cheers,
Clayton