TOPIC:

I had an AMCCO (?) two-point guard for a long time which cleared the case ends by about 1/2" - 3/4" on my '80. I've seen a 3-point mount with an additional long brace that runs back to the rear of the engine (frame). Regardless of 2 or 3 point mount, your assumption about the left hand alternator width is probably correct so spacers and extended bolts will be required as you've noted.
Depending on the gap requiring spacers - consider some 1/2" drive sockets (3/4"?). Chrome ! Shiny ! Rust resistant !
I had these.

Yes, that's what I've been thinking.

That's what I have. Can't install them unless I find a longer mounting bolt. (by an inch - inch/half)

Found a set of 3/8" drive that has a pass-through that is large enough. Naturally you'll want "Made in Japan", metric, ones !
You may have to get "a Shop" to cut and extend those bolts

No hurry there, will be probably the last thing to do on the bike..
So far I feel very comfortable handling it and not afraid of dropping - been moving around sitting on it around the parking lot quite a bit!
But I'd like to have the guards eventually - just in case of unexpected. Never mind the engine, although an innocent slip at slow speed could end up with a cracked cover in the middle of nowhere or South the border, and then what? ... Plus, they do save feet in such cases as well. So... guards and windshield for me is always a priority to have, especially on a bike which I ride often.
I'm sure I will find the right bolt once I will start looking for it.

Don't know if this would fit Stan, but you could consider using a 'joiner' to fill the gap.
Screw a shorter length of stainless studding (same threas as your bolt) into the exisiting hole, with (for example) half of the gaps' width of thread left exposed, screw on a stainless joiner (an internally threaded tube or hex bar) to act as the 'bolt head' plus tapping for the engine bar mount, then finally use a much shorter bolt to clamp the engine bar onto the joiner.

This type of joiner is very commonly used for cable trays in indutry, which are often suspended on studding (threaded bar).

Might be an option if those parts are more commercially available.