Here’s what I’m thinking. Drill the outter hole all the way thru, tap it, get a longer bolt with a nut, and do it that way. Thoughts?? I’m having to wrap it up on a budget so this would probably be a temporary fix for now!
It's risky but you could. There are some 3 bolt starters that would spread the load but they're pricy.
https://www.summitracing.com/parts/sum-820323-os for example.
Remember, a Chevy starter will try to break the starter bolts every time you hit the key due to the passenger side mounting location.
The plate and other starter can be installed by splitting the trans from the engine by using really long bolts (7") in the bottom 2 holes allowing you to slip the starter plate mostly in place and retain the bellhousing to block alignment.
When it's close take out 1 bolt and put it through the plate into the block then do the other one.
If you decide to drill the block the 3 bolt starter can be used as a drill guide. put a piece of 3/8" hard fuel line into the starter and put the 5/16" drill bit inside it. That will help to keep it aligned for drilling and you can then tap it the same way using the starter hole as a guide.
If you completely ****** it up you can fall back on the plate.
Good Luck!