However, it looks like all the bolt holes for fitting a hydraulic detensioner are still present, though I've no idea if it'd be possible to drill though to an oil gallery to supply the necessary pressure for it since the casting in that area has changed.
Unless I've missed something or someone's tried similar experiments in the past and come a cropper, that opens up something really interesting for 116 GTV and 75 owners - theoretically you can easily convert a later-type engine so it won't foul the bulkhead. This means you could fit a 3.2 'GTA' type engine with minimal modification to the cooling system and none to the bulkhead at all! You would need to do some engineering around the oil pump issue, though that'd be no problem at all for a race engine since presumably it'd be dry sumped anyway.
One other interesting difference - the 24v block has extra drillings in the main bearings leading to spray jets mounted beneath the pistons, whereas the 12v doesn't. Wish I could reverse engineer that bit...
Ok, on to other comparisons.
Unsurprisingly the inlet and exhaust ports for the 12v and 24v are completely different. 1-0 to the later 24v. Or is it?
12v and 24v plenums are exactly the same size, apart from the mounting and 'bling' the only difference is the later 24v has a different mounting flange for the throttle body.
And now for the interesting bit in this; good for me, not so good for 24v owners. The 24v trumpet size exactly matches the 12v inlet, there is no step whatsoever.
And also the 12v 164 inlet has exactly the same bore as the old 116 2.5 GTV inlet too.
So that means the 3.0 24v which should theoretically be able to suck in much more air through it's extra valves and increased displacement, can only breathe as well as the venerable 2.5 12v! Bet a few horses could be easily released from a later 24v simply by fitting it with a bigger plenum and trumpets which actually fit...
Finally, the common bits. Everything from the front end of a 12v will just bolt on to a later 24v; that came as a surprise too.