Test Start?

[C.I.Blazer]

I have put a lot of time and money swapping this motor into my Blazer and I am a little nervous that I am going to do all this work and the motor will not run. The motor I am installing is out of a wrecked Yukon. The seller did send me a video of it running before he pulled it, but of course I have no idea if that was the actual car or not. The motor is very clean, spins freely, and passed a leak down test I did. The shop that swapped the output shaft on the transmission said it looked like like it was in great shape.

I would love to do a test fire of the motor and see if it runs even for a few seconds before I continue putting everything back together. At what point is it safe to do that? The motor and trans are installed and by this weekend I should have the wiring all connected albeit not a super neat installation at this time. No front accessories (water pump, alternator, power steering pump) and no core support/radiator. Exhaust manifolds will be installed this weekend but at some point I will have to tow it to a shop to have the exhaust done. Finished the fuel system last night.

Would it be safe to fill it with oil and transmission fluid (no cooler lines yet) and give it a test fire? I would do my best to prime the oil first. Obviously I would not run it for more than a few seconds so I am not too worried about overheating. Do I risk anything with the PCM. It would not have o2 sensors, the alternator, or the MAF hooked up.

What do you think? Try to start it or just keep installing everything?