Hia, I'm running two Alfetta GTV's... same basic tranny in the back (but without the limmy and the flash gear linkage).
! has a 2.0 tranny, the other has a 1.6 tranny... both started their lives as 2.0's.
From what I can see their identical in everyway, but think the ratio on the 1.6 is slightly lower, the range of each gear is very similar, just the 1.6 has slightly shorter legs.
For track use the 1.6 would be great, but is very tiring to drive any distace as it's always reving, where as the 2.0 tranny is much more suited to dual carrage ways and has a far better top end speed.
As for the four/five bolt thing.... just change the drive flange's, drive shafts are all the same (par the V6's that have a slightly different set up)... the tranny should fit and bolt up exactly the same