My cousin did this conversion a while back. Bolting in a 2TG is very easy.
You gotta use the existing 2TG engine mounts, the 3T ones dont line up properly form his experience. And use the T18 box so the shifter lines up. Connect up hoses and the minimal electrics and away you go. Only problem was the accelerator cable, but some form of Corona one fitted well.
I reckon just stick with the stock 2TG with some extractors. getting it all rebuilt with big pistons and the works will cost a fair whack. Just enjoy it singing away to redline day in day out.