sorry dodgeman, obviously i havnt made myself clear enough. thanks for pointing it out for me to fix. this is just what i have found.
The alternator bracket is off an early model a12 (dizzy at front) with the alternator on the left hand side of the engine (as sitting in the drivers seat looking forwards). Trying to fit it to a15 as i want to run alternator in same position.
Mount/braket didnt fit obviously as the block wont allow.
Wont allow becuase the tapped holes in block are wider than the holes in the bracket/mount from alternator.

So i slotted the rear hole of the mount/bracket to get the alternator in line with the crank pulley and waterpump. Slotted front hole in mount/bracket so that it fits with the hole in the block.
So we have the mount in the right position, the alternator in the right position.
Now, i meant the coolant inlet on the left hand side of the engine as looking from the drivers seat towards front of car, surely you must have realised what i was on about. No need to be difficult.
Anyway, this is longer on the a15 than on the early a12's. Because its longer, you can either cut down the inlet and hope there is enough room to not have to modify alternator adjustment arm or you could just modify arm straight out of the gate.
This is what i did by choping arm in half and adding a section in the middle.
The a12 drive belt is shorter than the a15 one.
But the a15 one is too long for how i've set it up (alt on the left) and the a12 one is two short.
Solution, i need a belt 20mm longer than the a12 one. a lot of shops that sell belts should be able to help if you have the a12 one.

Anyway, those are my findings when trying to fit alternator on left side of engine with alt bracket from early a12.
Im just writing down my findings to maybe help someone else out there who may be wanting to do the same.
Also for the record, im putting alt on left side as the nismo oil pump on the a15 wont allow alt on normal right hand side.

Hope someone got something useful from this and it made sense