This isn't a stock starter, it is similar to the one posted by derek, but I knew I could count on summit to ship immediately, so I went with them:
https://www.summitracing.com/parts/pwm-9100

Yes... it came with the right bolts, or at least bolts that would work, but there was nothing special about them. I knew the holes could accommodate more threads in them, and I also wanted to source grade 8 bolts. Given how far OEM went on bolt design I figured it was worth additional thought given the reason I'm in this situation is because they broke. In the end, the only thing that could work was a similar bolt (plain allen head bolt), but it had about 1/4" more threads. Not really a ton of gain, but I measured everything and they worked. Fastenal was the only place that had something, but it was still just an Allen head. I asked what grade they were, and she said all of their allen head bolts are something like a "grade 9", so, I'm not sure what that means, as it isn't a grade rating for SAE bolts and I question if she knows what she's talking about.

What I would have liked to have is the bolt shaft extend slightly beyond the starter housing, so it could partially center in the recessed non threaded portion of the block, similar in purpose to the stock starter bolts. As derek had eluded to earlier, that would have required getting a much longer bolt, then cutting the threads.

So, how well did it go in? Not exactly perfect. The inspection plate (or, dust plate I guess) got in the way. It was designed very specifically to accommodate the stock starter. I had to grind down the edges on the outer side of the starter frame to fit. On the inside, I'm sure that the dust plate is in the way as well, but I think it had more give where it was at, and I was able to thread the bolts in relatively easy. On the outer bolt, the dust plate sat between the starter and the bell housing (or whatever it's called) just a little bit, as the frame on this starter was wider. The way this starter was designed, it needs to be flush. I ground an angle on that side of the starter housing about 1/8" in, and that allowed the little bit of space it needed to fit past the dust plate and mount flush. Without doing this I couldn't even get the bolt in. I suppose removing the dust plate might have been an option, but I wasn't sure what that would involve or look like in the end. I'm still not 100% sure it doesn't sit slightly at an angle.

...in retrospect, with all the effing around I've done with this thing, if I had just dedicated a day to it I'd probably have had the engine pulled, fixed the stock starter and have it back in the boat. It would have been a long day, but I bet it would have been less painful than trying to fit my fat ass in that engine bay while try to messing with this starter.

So, it is "in", I was ready for whiskey by the end of the day anyway, so it isn't wired up yet. Tonight hopefully I'll have a chance to wire it, cross my fingers, and give it a go. This feels like a bit of an experiment, and that isn't a great feeling when you're in the middle of the lake.

Ayuh,.... The knurlin' on the stock starter bolts centers on the starter housin',......
Not in the block,....
The relief in the block is wider than the starter housin',....

'n grade 8 bolts aren't necessary, as the torque on a 3/8"- 16 bolt is 'bout 35 ft. lbs,...

Starter bolts break when they loosen up, not from starter torque,.....

'n Yes,... Allen bolts tend to be rather hard bolts, probably grade 8 or better,...
Oil quenched, 'n hardened,...

Good info, thanks

So, I have this thing installed, then went to test it out and I have no voltage to the dash gauge, and no power to start. All other electronics work fine. There was a main power wire that when to the main terminal, along with a second wire that was maybe 10awg, then the smaller one that went to the small terminal for the solenoid. There isn't much to it. What could I be missing. Is it possible this starter doesn't ground well?

most likely a 3rd hot wire goes to batt terminl of solenoid. hanging in the bilge. or possibly the red circuit breaker tripped. that'll shut off the whole boat.

I'm too embarrassed to tell you what it was, but I think you already know.

when anyone does anything and something else goes wrong. they just did it...how does it work?

Just gave it a test go.... we have success! No bad sounds, cranked over nice. Maybe even faster than the old starter.

Was a good feeling to hear that rumble again. Thanks for sticking with me through this thread.

Enjoy.

so far so good.... got me through a few days of boating; however, once in a while the gear does not connect, and simply spins against the flywheel. 9 out of 10 starts it is fine, and doesn't sound out of line, but the other 1 out of 10 it'll just hit the fly wheel and spin (or at least that is what I assume - light grinding sound, engine doesn't turn). Most of the time there is no issue, and it seems to be occurring less and less (that could be in my head), but I feel like I need to pull this starter again and trim it with one plate.