I'm not really keeping up with the thread but I wrote this in moments between too many meals and too few cold drinks I was listening to new to me music.
The square and true fitting of the rear mount to the seat tube really cannot be compromised under any circumstances .. imho but nah not mho its just essential. Instead of tilting the engine though, there are options for moving your engine further forward. You can use a little piece or a few layers of cheap alloy flat bar with two holes drilled in if to put it over the rear studs, then the mount that you get in the kit.
Longer studs might be necessary, but studs are just bolts with the heads cut off. Get decent ones check they're long enough, cut em off and clean up the threads a bit. Install the cut end into the engine snugly not torqued, with red loctite.
Stack your flat spacers and the saddle mount, install to frame, add the outer strap part if the saddle mount without any compressible material.
Tough plastics can be used on place of alloy shims, but nothing rubbery and compressible is recommended.
Use the double nutting method to put only the recommended torque for
your studs' thread into cast alloy onto the first nut then, by holding it against turning, you can make the second nut good'n'tight.
M6 thread studs should be torque to only about 60-70
INCH pounds. That's what correct double nutting sorts out, isolates the final nut and stays secure.
M8 are better of course it's a big 100
INCH pounds jump in max torque you can apply, and if you have a newer model of engine with a headless cylinder then I have no idea what the thread standard is on that.
Some people put bolts into the engine. Unfortunately this is the only way sometimes with fitting certain parts to the engine. It is not my preference.