Low compression on 5.3 swap

[Jason Banks]

I would do exactly what you say. Get it running and see how it goes. As painful as it sounds, it could always be pulled out later and fixed.

I'd say it needs to be good and lubed up....oil on the cylinder walls, to get a good reading. You probably won't get it coated well just by cranking with the starter. Some fogging oil might help - https://www.amazon.com/STA-BIL-Rust-...dp/B000H7CKAY/

You might get a borescope in the cylinders and see how the walls and valves look. Here is an inexpensive one that has multiple cameras on the tip so you can see different angles. There are many other on the market, this is just the first one I came across:
https://www.amazon.com/VEVOR-Triple-.../dp/B0BVMFYQNS