Thanks for the reply. I have tried using the tools on the European ROM, using "recompile Bottommost" but again I get a checksum which is different from the European ROM patched with the IPS file. If I apply the gun hex mod it still doesn't match. In the readme for the PC Conversion you suggest...
Which specific Doom II ROM version is the IPS patch intended for - the USA one or the EUR one?
If I apply to both they each still appear to function when tested in VisualBoyAdvance, the game doesn't crash in the first level so it's not obvious.
If I use the Doom II Modding Tools method (with or...