Can anyone advice me where I might find a Head gasket is for an Ford pre-cross flow 1500 GT bored out to 1670cc.

we've Tried Burtons

X-flow and pre x-flow head gaskets are the same and that includes BDA and twin cam variants. Any gasket to suit a 83.5mm bore will be fine. Thickness is more important, you need to keep the same compression ratio and valve clearances.

Surprised Burton cannot sort you, here is a link to their gasket page http://www.burtonpower.com/parts-by-fitment-type/parts-by-engine-ford/ford-pre-cross-flow.html?part_type=625&product_area=745&product_group=24 2 it shows lots of choice of thickness and bore size.

Only difference between a x-flow and pre x-flow are the inlet and exhaust manifold gaskets.

Have you tried throbnozzle racing?

Past Parts in Bury st Edmonds may be able to help