Repro radiators fit perfectly if you buy one designed for the car. The fitment problem comes into play when you go out and buy one of those Rodney Redneck brands. Also, you get what you pay for, the reason the correct repro is 3 or so hundred dollars more than the Redneck brand.

Back in the old days, a rad shop would tell you whether it could be repaired or a re-rod, and you could rely on their judgment call.