there is no early vs late A12A -- it was only made 1978-1982. It's a totally different casting than the 1978-1982 A12 -- some say the cylinder walls are larger (so not bored out from the A12 size, but actually cast larger)

56-series 4-speed is 28 lbs lighter than 60-series 5-speed. Engine-wise, A12 is about 13 lbs lighter than A15. The main difference is 15mm taller block, otherwise exterior dimensions are the same

Colin was right of course