have a standard 1300cc crossflow fitted to my locost (711 block), I now have a 1600 gt head to fitt . The problem is that the 1600gt head has small chambers and I think that my 1300 head is flat I have not taken it off yet. Will this be a problem and will it lower my compression ratio.
Help

That must be a very early 1600 head, best to pension it off I am afraid.

yes iirc
later x-flows had flat faced heads and cut outs in the pistons....
early ones had a continuous land arond piston and a chambered head
i dont think it would wise to mismatch them i think you are right and you would lower the C.R some good advice from your local engine shop might help or they might be able tosupply the right pistons for the alternative head
cheeers les g