GM Barrel for T/C Cougar

[Johnny Reb]

Hey Everyone,
I want to buy a new barrel for my T/C Cougar 50 cal caplock. The barrel in the T/C cougar now has several pitted areas, and it's never shot anything consistent. I like the Green mountain barrel in 54 caliber 1:70 twist. so my question is, the Gm barrel is 4 inches longer, will this upset the nice balance this rifle has? also Gm says their barrel is a drop in replacement, is there anything I may need to do? they say it should fit without any modification, at least I hope so. Thanks in advance for all your input.

Regards
Johnny Reb