exahust size

i have a 90 go 60 good conditon but the guy before me holowed out the cat. so I i was wondering what size pipe i should use. i came across a 3 inch cat and was thinking about going 3 all the way back. would there be any problems with that or should i go smaller? plese help :confused:

If you can cram 3 in under there then go for it. it cost a shit load but you wont be dissapointed