Auto engine bolt patterns

Hello

Does anyone have any experience getting the bolt pattern off the
transmission side of an auto engine?

I'm building a PSRU, and I need to make the plate that bolts to the engine.
The rest of the pattern is generic, but that is engine specific.

I have tried several ways of measuring the holes in the block, but I'm sure
I can't get accuracy better than 1/10 inch or so. Surly engineering drawings
for these patterns are available somewhere.