I agree Tom,..I've thought the same thing in the past,..I made a mounting frame from 1" square tubing for my 13 HP Honda and the holes are bigger than they should be simply because I didn't get them quite right the first time. I used spray paint and one of those red WD-40 straws and stuck down in and sprayed,..thought I had it, Ha,Ha,...So I had to make the holes bigger to make up the difference.
Measuring never worked for me neither,Ha,Ha,...
When I bought a new Honda GX 630 this year, I was glad to see the mounting holes were the same and I was able to reuse the same frame.
I remember looking online for a template,.couldn't find one. I guess they sell them as replacement engines, so in their mind, the holes must already be there.
Jeff