If you're going to do the belts, then a head gasket isn't a huge deal more work.. may as well get it done and sorted.
For the sake of saving a few quid, I'd use a genooine parts head gasket.. The one that arrived for my '55 was made by Victor Reinz .. and Reinz sell their gaskets under their own name as well as in the AR packaging. Search for a distributor.
The other gaskets you'll need (exhaust, inlet manifold, rocker etc.) are less crucial or simpler to change if they start leaking, so a regular auto factor should have a kit.
When your beast is in bits, use parafin to clean off the brown varnish.
Ralf S.