The sealing surface area is indeed smaller, still I think it’s as much as in XJ engine, so I hope it should work.
Water pump side may need some welding, as the surface for the seal is even smaller there.
Where are you located? I have a front cover left over from a XK150 3.4L I scrapped (cracked block).
Waay over the pond, i.e. Poland, EU. 
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