Hey Tappet if your shifter is only 2" further back the engine must be a fair way off the firewall??? Either that or a shorter gearbox??
I have just fitted a CA18 box into my coupe It has replaced a MR30 skyline box, its sits closer to 4-5" further back. I had to relocate the handbrake cable.
The gearbox is also quite wide at the back so you will either have to widen the tunnel a bit or just let it rub and vibrate on the bodywork. (not a good idea). I suppose it really depends on how high and hopw far back the engine and box sits back.
The crossmebers I have been doing sit really low and the head is only 10mm off firewall (easier to get to gearbox bolts and better weight distribution.
cheers Andrew