Not just Monaro got a trimatic, you'll find them in Premier, Brougham, Belmont, Kingswood and GTS. Pretty rare outside of GTS though and never in GTS350. You can modify a Powerglide one - there is a guy that sells the piece with the detents on it on Ebay to suit Trimatic which will also suit TH350. Just the console insert reads wrong. If you ever find two console inserts let me know, I'm probably going to put a TH350 into the yellow 307 auto car initially at least and I only have a Powerglide console insert.

I have heard a Cortina one fits in the hole where a manual HK-HG console insert goes.

HK Tonawanda engines were the same design heads as the 307, just Tonawanda's version of them. 1.72/1.5 valves, small ports and 69cc chambers. 3917290 casting. The McKinnon GTS327 engines were 75cc chambers, same valves and ports, 3927188.

GTS350 manuals used Fuelie heads, they weren't double hump as Tonawanda didn't use the double hump mark, 3947041. The last of the HG engines from McKinnon used double hump heads, 3973370, these were bigger intake port heads.

GTS350 autos used a 75cc head, same bottom end as the manual engine just the larger chamber heads, 3932441.

They are but that doesn't affect the performance, just the durability. Same pistons and camshaft, only variable between the LM1 and L48 as we got them respectively for HT-HG GTS350 auto and manual was the heads and the initial dizzy timing specified.