I've got the radiator out of the XJS and thinking about a swap since originals go for $600-700 dollars and aluminums are supposed to cool better. Didn't see any threads where its been done but doesn't look to awful hard if measurements match. So far it sounds like aluminum dual core is good cooling design. So far i've found three that sort of match up:
1963 Skylark (except output hose on opposite side)
1994 XJS 6.0L V12 Coupe
I don't see any concerns. I use a custom made one on my racing XJS (6l engine) with no issues. Just imagine V12 6l engine running constantly over 4000 rpm with no overheat at all. I can provide you with a piece identical to mine but you'd need to modify holdings since the radiator I use is smaller than original. Provided you'd be interested in I can send you my price and lead time quotation.