Like cosmic says you should not use a matching bore size gasket (use the oem gasket measures to give you idea of required difference), closest you would probably go is 0.5mm, example being I use 87mm bore HG with 86.5mm bore block, Tomei also used/supplied gaskets around 0.5 to 1mm bigger bore.
Gasket protruding could catch piston & also is a heat spot det risk, too recessed gasket is also an issue for heat spot det .
I don't use cosworth much as they not easily sourced or as cheap here compared to UK, apaxi & tomei cover good size options & are about £30-£40 more than UK priced cosworth for me in asia but probably far more in UK/EU . might be worth contacting cosworth for full size options or seeing if will increase size range.