Disco 2 Intercooler upgrade auto

Hi all, is it possible to just bolt on a larger intercooler from a truck to my td5 auto and get the same benefits as other upgrade intercoolers?
Is it generally bigger volume = more cooling? Or is there an aftermarket one that doesn't cost 400quid
Will a 2003 td5 pass an MOT with no CAT on the exhaust? Hmm probably not but does anyone know for sure?
Recommended air box spiral thing removal?

All of the above am looking at before I call Mike from Dynachip for a remap.

Gods but i've spent some time searching lol

My 2002 td5 15p passed with no cat and EGR gone this September

No CAT and EGR blank SHOULD be a 'Major fail' from this year but so far I've only read posts where they have passed without any issues as did mine with total EGR delete.