Use the R4 rods 38mm and 1 1/2" phoenix crank yes.
I thought there was a 56mm piston made for export market R4's,maybe someone can confirm this?
I would have the block bored to suit the 58mm pistons,If it is ok,no porosity use it.If you need to liner it you may need to consider using Austin or rosengart rods and readily available smaller pistons if the 56mm R4 pistons are unavailable.
There is not enough metal in a standard block to reliably use the oversized liners in my opinion.

Location: Channel Islands

Dave, I believe the early Renault 750/4 pistons are 56mm. I am running a set in one of the specials in a standard bore block. Someone who knows more will probably be able to give chapter and verse.

Regards,
Stuart

I understand Alex - I shall be back in the workshop in the new year and can measure a liner for you then, if nobody else does so before then.