For what its worth,
I bought a mini starter for my sbc from Pace that came with bolts that did not have the knurl towards the thread end. My understanding is that the knurl fits tightly into a counter-bore in the block and the starter bolt holes to reduce/eliminate any clearance that would allow the starter to move sideways, sort of like a dowel pin.
I also wanted a starter brace, but could not find one for a mini starter. So I decided to try to make as tight a fit as I could for the bolts. I had previously ordered some ARP starter bolts for a sbc before I bought the starter, only to find that they were too short for my mini starter once it arrived.
I decided to try 2 mods. 1st I put counter-bores into the starter block that would enable the use of the ARP bolts. I used a 5/8" end mill(I have access to a vertical mill) to mill a hole about .405" deep into the starter block that let about half of the bolts knurl to extend into the block. I admit that I milled one bolt hole that I didn't need to as you can see in the pic.
However, the knurl was still loose in the starter block. 2nd mod was to put a 3/8" ID bushing into the starter block that was a tight fit on bolt knurl. I used a 1/2" end mill to make a .550" counter-bore in the starter block where the knurl protrudes. I bought a bushing (3/8" ID, 1/2" OD, x 1/2" length) that I pressed into the block. It was a tight fit. I reamed the ID of the bushing to .375" as it compressed somewhat after the press fit. The bolt knurl measures about .380", but since the bushing is bronze I think I can get it through with a little effort.
I didn't try to bush the other hole as it was not a flat surface, so I only have one hole that is going to act like a tight dowel. At least the other hole will have a knurl in the block.
I know its probably massive overkill, and I haven't tried it yet, and most don't have access to a milling machine, but thats what I did. Maybe you can get some alternate ideas from what I did. Good luck!