It is relatively easy to fire these up out on the ground. In fact, years ago I would always fire them up like that before painting and installing them. Nowadays, it is the local speed shop's engine dyno. Just a spare tire under the pan along with a spare trans or bell. Never had a problem doing it but did find an issue or two. Mostly oil leaks that were easier to address at that point.

I haven't installed any engine fresh or not without test running them in over 40 years. Installed one bad used engine in the early 70s and that was enough for me.