Rear disc conversion and master cylinder

[homemade87]

I did rear disc to my 82 truck and was going to change the master cylinder to a disc/disc to try to get a little better peddle . I did a little research and seen where some was using the corvette master so I ordered one . When I pulled the oem one off the bore opening was much larger that the corvette master. The one I ordered was for a 70 something to a 82 corvette. The booster has a much larger hole so the vette master will not fit like it should . Is this what some of you are using and just bolting it up.I did not know if this would affect the rubber seal in the booster. Heres a picture of what I am talking about. If anyone has a better solution I would like to here it.