Simple to resolve mate if its a new block - and people are correct new blocks are unstamped.

Buy a set of stamps from Machine mart and stamp it yourself with a unique number- not illegal as you are not trying to hide an old number -and if the number you decide to stamp it with starts YBB or YBG then guess what its then a pre 92 spec engine for emmissions purposes so no cat required.

A lot of people use an early YBB block to also get around the emmissions regs for sva