You want these little nylon standoffs that were common in the day.

Ah this makes complete sense. Thank you.

Mostly those, and maybe 1 or 2 screw positions to stop it sliding

Yes, screw standoffs whetever they will go and these plastic ones everywhere else.

Really depends on case and board combo how it goes, these holes were not very standard. Sometimes you have to cut the hook thing that hooks into the tray off if the motherboard hole does not align with case, just to have a foot under the board so that it does not flex too much.

But sometimes they fit rather well. When two or three screw types align and the rest of the plastic fits, it works great.

or do what many did back on time... just put a cardboard (or a old magazine) behind the board and thats all. The ISA cards will do the rest