Do you remember the bolt circle dia. you milled in your blanks?
Sorry, I don't....I knew I should have saved that bolt pattern info!
Hindsight is always 20/20. The rears were easy to measure (square 4 bolt pattern), the fronts required a little trig to calculate the diameter. (3 bolt pattern) The hole patterns in the rims were a little inaccurate (at least by my standards) so I measured all the holes in each wheel, both inside-to-inside and outside-to-outside, and then averaged them to get the proper spacing. I counterbored the holes to allow the square under the carriage bolt head to "bite" in the cast iron, and set them with a hammer rap at assembly. Interestingly, the rear valve stem cutouts where in indentical locations, while the fronts where about 10 degrees different from each other.
The standoffs were cut from 1" aluminum tubing with a .250 wall. (leaving a 1/2" hole for the carriage bolts) And, again, I should have saved their dimensions. One great thing about a project like this is that things can be pretty sloppy and still work fine. As a friend used to say "We ain't buildin' a church here!"