Transom Holes

[umecheme]

Getting to a point where I'll be drilling holes in the transom.  I have the old holes to go by, but want to make sure I keep everything straight, and don't want to have to be wallowing out holes to make them fit.  I found jigs for Evinrude transom bolt patterns but they're crazy expensive.  I'm sure someone on here has a crafty way they've done it to be super accurate.  What's my best approach?

[umecheme]

P.S. I'm trying to not put the outboard on the boat to do this... I have the outboard in a separate garage, and its going to be a process to move it from the attached garage to the detached garage.  Might be easiest to mount the motor with bolts to a 2x12 in that garage, then clamp the 2x12 flush with the top of the transom and use that as a template? 

[umecheme]

Also, by how much are people over-drilling these holes before they refill and re-drill?  3/4 inch hole for a 1/2 inch bolt?

[dbiscayne]

print this out to scale

[umecheme]

Exactly what I was looking for, thank you!