Skidlids,
I think your a bit rash butchering a 748RS exhaust system. Bear in mind it's a £3000 system. Why not sell it and buy one for a testastreta?
54mm 996R/998 Exhaust Made by Sil Motor and from what I've heard, every bit as good, if not better than Termi and you could always replace the stickers with Termi ones.
Bit of a bargain at the moment and I'm sure you could sell the 748RS system for plenty dosh!
Just a thought . . .
Neil.