I am looking to do a LQ4 swap. My plan is to build a street/strip nova.
How many miles on the donor is still acceptable? I found a complete suburban with 140, but didn't know if that was too high already.

 

If the engine was well maintained, 140k miles is nothing. If not, the engine could need a rebuild after 40k miles. It's hard to give a definitive yes or no just based on mileage.

 

Yea there is really no way to tell what kind of shape one is in without a tear down. Best thing to do is do a compression check maybe a leek down test. If you can pull the oil filter cut it open take a section of the filter and squeeze it in a vice to press out all the oil and see if there is anything in the filter. Really thats about it mine had 80K on it when i bought it and only thing i used was the bottom end and i did not touch it and its still running strong.