[tcrist]

I don't think anyone's insurance company would approve a non-employee to be there working / assembling.

Also, what if the owner doing the assembling were to drop say a a part, say a piston, cam, or even the block. Who would then be responsible. If they got hurt, that would be a whole now can of worms.

As mentioned, the time it takes. You tie up a employee for two to three times (or more) as long to do this job. It would be different for every engine depending on how much the owner knows about mechanics. It could be like teaching someone that doesn't even know what a socket is, basic automotive technology. You could not even quote the cost to the customer/owner.

JMO, of course.