I have been looking for a used 45-120 black powder rifle(cartridge)

I have a pedersoli 45-70 now..How much of a job would it be to re chamber
it to the 45-120? Or maybe I'd be better off to just buy another 45-70 and
do the re chambering to that one...Then I would have the double set
triggers I want on it as well as the pistol grip stock...

Here's a place to check on Reamers and what it takes to do this job.

http://www.4-dproducts.com/display.php?group=Rifle+Calibers&PHPSESSID=45efb7f7d032e8883471737a383d1a8d