Yes to all. Although the SBC design engines have unique mount adapters the actual engine crossmember “posts” where the mount adapters (or the mounts themselves in the case of 6cyl and 253/308) bolt to are the same across HK-HG. You also don’t have to use HT-HG 253/308 engine mounts and engine mount plates, HQ-WB look a lot different but work identically. Just don’t try and use Torana or Commodore mount plates as the engine then sits differently although the engine mounts (rubber bits) are common between the three.

The major subframe difference is the HT-HG have the extensions at the back for the gearbox crossmember whereas HK uses a HD-HR gearbox crossmember. Also the first half of HK have a different RHS inner guard that you have to use a lever type brake booster, the later type have a clearance hump to suit the straight pushrod booster. HT-HG subframes are missing the HK grille mounts too.

There is a difference in where and how the HT-HG column shift indicator goes and works as compared to HK. From memory if you just bolt a HT-HG auto column into a HK there is an interference between the HT-HG indicator and the HK dash plastic. What I think most do is use a HG Trimatic shift gate (and associated linkages) on a HK column which gives you the Trimatic shift pattern. And you then add a 2 in the appropriate spot in between L and D on the plastic part that clips on the HK fascia, or buy the part already made:
https://walmatdesign.com...ator-Selector-p388461113



Here is the shift gate:
https://www.hkhthgpartsa...t-gate-and-selector-arm/