Hi,
See if you can get pictures of it. If it has the long header tank that positions the filler cap about 12" rearward, and I think it will, it will work. Even the early TR4 rads (same time frame as the 3"B" were being built) had the same, long header tank as the 3A. So, my best guess is, yes, it should be fine. The only thing I'd try to avoid is the rads with the hand crank hole. That hole cuts off about 20% of the cooling and can cause overheating problems. A rad can be rebuilt without the hole, but that's an additional cost.
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