In your post, you cite the reason for replacement is that its "getting pretty old". True enough, but does it leak or overheat, or perhaps have broken side bracing? If it doesn't leak, you could always just get a proper flush and likely be fine.

Keep in mind that any boneyard radiator will likely be just as old, and probably in worse shape for sitting idle. So if the one you have works for now, I'd think about sourcing that boneyard unit and have it re-cored and on hand for the rainy day when you actually need it.

In your picture, I don't see any badging to suggest its an auto, but if it is, you'll need a radiator from an automatic donor car.

-Matt
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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC