How do you know how many miles are on an engine w/ out odometer?

 

Easy answer. You dont'.

Some things to look for though. Do a compression test. Pop the valve cover and look at the condition of the valvetrain (if it has brown sludge all over it it's an indication that the oil wasn't changed often enough). Do a leak down test. If you want to really get into it you can remove the oil pan and look at one of the rod bearings. Also look for gold colored metal flakes in the oil pan (a sure sign of fried bearings)

Mike