[RICK LAKE]

Large Arbor Goggle on youtube how to align a bellhousing. I think you already have adjustable pins to move it around.The pins are offset, some are .004" up to .012". They sell 3 different off set pins I told you that you can cheat my moving the bellhousing to the left of the block. Max is .010". The idea number is .000" This is in fairy tales. Getting down to .002" would be great.
Your choices for getting the starter to have full engagement is either go to a machiune shop and have them mill .150" off the mounting location of the starter or start with cutting out the block plate and retest the depth. The milling is not going to be cheap and the problem I have with this is the thckness of the mounting housing and not having it crack at the bolt holes over time. Also with this custom work, you break down, you can't goto the locate Pepboys or Autozone and get a customer machined starter. The white metal on these starters is marginal at best. Sammmy did this to his starter for the same problems you have. If the machine work to the starter works, great. A couple of years down the road you could need another starter and you are back in the same boat if it's not the bendix. You could get this starter rebuilt if they can get the parts.
Other thing, I use MSD parts in my car because at the time a was building it there was not alot of choice. Today everybody sells mini starters. I would still carry tool box and parts parts.
Align the bell and cut the plate would be the easy way. You again might have to slot the mount holes on the starter just a little to get down to the spec for teeth to teeth contact gap. I like the studs and nylocs with washers once you get into spec. Last note, the starter ring gear may not be 100% true in spinning. I have seen and found high and low spots as far as .020" out. You might want to check this also. There's not alot you can do to fix this problem. Good luck Rick Ps cutting the block plate will give you more engagement of the bendix teeth into the flywheel teeth. Less chance of breaking off teeth and having a sour sounding starter up. Plate cutting gives depth, slotting the bottom hole on the starter gives tighter air gap. May need to oblong the other hole to match the adjustment. Take as little material off as possible if slotting is done. To know how much material to remove from starter, spray a little paint or use a touch up paint and apply into the hole, add a 1/16" for clearance and expansion of the motor between hot and cold.