21 stud main cap bolts

Agreed but we are looking at the early evolution of the flathead v8
I do plan on substituting with socket head cap screws with hardened washers
Had also thought about the possibility of threaded inserts and studs but considering these engines have been around for 85 years figured wasn’t necessary for my speedster application see my avatar
Yes I have a 3” center to center dimension
 
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The '37 chassis parts catalog suggests that it might not be that simple. 18-6345, bolt (crankshaft bearing cap) 8 cyl., is listed for '32 -'36 for BB, 18, 40, 46, 48, 50, 51, 67, and 68. and 40-6345, stud (crankshaft bearing cap) 8 cyl., is listed for 1932-34 for BB, 40, and 46. Plus 48-6345, stud (crankshaft bearing cap), is listed for '32-'36 for BB, 40, 46, 48, 50, 51, 67, and 68. Lastly, 68-6345, stud (crankshaft bearing cap), is listed for '36-'37 for 51, 67, 68, 77,78, and 79 with a double asterisk indicating that it is used with a large hearing crankshaft.

One of those listings might be in error, but all four and with assigned part numbers at that?

They suggest that studs started being used on a limited basis back in '32 engine production and that there isn't necessarily a correlation between vented blocks and their main bearing cap fasteners. (While I've seen more than my fair share of '32-'34 V8 cylinder blocks, I do not recall any of them having studs rather than square-headed bolts to attach the main bearing caps, which, of course, proves nothing as it is not a large enough number to be statistically significant.)
 
Not going to touch on inaccuracies in 37 parts books but it is not possible to use bolts in RF,RR or LR on vented blocks.
Will dig out my 1934 parts book and see what it says.

DavidG said:
The '37 chassis parts catalog suggests that it might not be that simple. 18-6345, bolt (crankshaft bearing cap) 8 cyl., is listed for '32 -'36 for BB, 18, 40, 46, 48, 50, 51, 67, and 68. and 40-6345, stud (crankshaft bearing cap) 8 cyl., is listed for 1932-34 for BB, 40, and 46. Plus 48-6345, stud (crankshaft bearing cap), is listed for '32-'36 for BB, 40, 46, 48, 50, 51, 67, and 68. Lastly, 68-6345, stud (crankshaft bearing cap), is listed for '36-'37 for 51, 67, 68, 77,78, and 79 with a double asterisk indicating that it is used with a large hearing crankshaft.

One of those listings might be in error, but all four and with assigned part numbers at that?

They suggest that studs started being used on a limited basis back in '32 engine production and that there isn't necessarily a correlation between vented blocks and their main bearing cap fasteners. (While I've seen more than my fair share of '32-'34 V8 cylinder blocks, I do not recall any of them having studs rather than square-headed bolts to attach the main bearing caps, which, of course, proves nothing as it is not a large enough number to be statistically significant.)
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