When you shoehorn a larger engine in, you always run the risk of cooling issues. They might have slapped a small e-fan into it which won't cut it for cooling with a 5.0. The folks that slap 350s into S10 frames have the same thing, and end up using a Taurus dual-speed e-fan or other high-CFM setup for cooling. Plus, a lower thermostat always helps.
I guess if you're curious as to what to ask... would definitely ask on the cooling aspect, which e-fan they used, etc. What they used to mount the motor (e.g., aftermarket mounts, custom mounts.. rubber or poly, etc).