I agree with those who advised finding a radiator shop that will you a rodding job, i,e, taking the top tank off, boiling the core with bottom tank, rodding out the flues and fixing the leaks after reassembly and testing.
I doubt many shops will do that now. If you do and there are minor, tiny leaks detected you can use some stop leak and that may seal up sufficiently for your purposes. "Solder Seal "come to mind.
My father ran a radiator shop for many years and installed new cores, if needed (Harrison for GM cars and McCord for Ford and Chrysler ones), but most went through the rodding process. A few flues that can't either be rodded out or have too much damage or rot can be eliminated if needed and still function satisfactorily. I worked and apprenticed with him from about 1944 until 1954 when I volunteered for the draft and did a two year hitch in the army.
I ran the shop from July 56 to February 58 when I closed it and went back in the army for 18 more years. (First good career decision I ever made.)
I still have a few old NOS radiators upstairs in the garage. I'll check to see what I have.
Best,
Charlie
BTW: Simply boiling over after a run may be the result of over filling the radiator and always caused by overheating owing to the radiators ability to cool as intended. Water expands when heated so you need to leave enough room in the top tank to prevent discharge of coolant when it's hot and especially just after stopping the engine. Owing to this water expansion factor overflow tanks were invented for the hard-headed ones of us who practice overfill filling because we want all the coolant in there that can be had. Generally the overflow tube will take care of the excess but it will make itself evident on the floor of the garage or someone's nice driveway.
BTW2: A back-flush may help some of the flues the have been plugged by rust but only the ones loose enough and necessary to succumb to the pressure and not the more stubborn ones. Usually a proper back flush even using a Kalamazoo water and air adaptor is just masking the problem and any success will be short lived.
BTW3: I wholeheartedly agree that removing the water pump and foundry molding residue access ports (freeze plugs) is a good idea. By itself not very effective. You can also back flush the block via the petcock at the rear of the block on the driver's side. Only thing is some of the smaller passages in the engine are had where the the head meets the block and thus will be difficult to clean except tank boiling with a chemical solution. Engine rebuild shops offer this service. But, well, you know, that entails a heap of decision not easy to be made.
BTW4: I also checked 1929-48 parts book and see that Gene was correct. As he almost always is. You know.