I bought a rad, shell and stoneguard recently. The rad appears in excellent shape, but before considering using it, I thought it might be a good idea to have it checked out. Most rad shops around here are just so-so, but I figure I should have someone look at it or pressure test it. So if I go to them what should I tell them, and what should I know. For example, do these run under much pressure at all? Is the rad cap supposed to act as a pressure cap (my cap that came with car is not original)? I hear what is likely a small amount of rust scale inside the unit, can this be blown out with air?

The original radiators ran with no pressure. If the radiator is an original honeycomb then have the radiator shop do a flow test but do not put it under more than a pound or two pressure to check for leaks since a new honeycomb will cost you $1,000.

Thanks for this advice, I will proceed very carefully. The original that came with my car is also a good one, so I hope to have two to rely on.

Also keep in mind that those radiators are 80 years old so they may be limited on the amount of cooling that they will do.