Bell-housing alignment help

I already had to egg the bell bolt holes to get it to even accept the 0.021 dowels.

Robb said CNC'ing a 1-off part would be absurdly expensive. More than $100. He suggested drilling out the alignment pin holes, bolting it on, beating on it with a mallet until it was aligned, drilling out some washers to be snug-fit over the pins, slipping the washers over the pins and welding them to the bell, to keep it from moving.

have you tried mounting the base to the back of the block and checking runout on the crank flange, both for flange(flywheel mounting)surface flatness, and for edge runout?
if there are no surprises there, then I think I'd try it with the .021 offset dowels. I guess you'd like to get it perfect, but sometimes close enough is good enough.