Fingers crossed for you 3DM, it will be rather interesting to see how this this old girl really goes.
I totally agree with what you had to do to make it work, virtually giving it a bit more 'freebore' so to speak, the chamber is still original so it is a win-win for you mate.
It would seem that with a larger case capacity than the .244 Rem, you should get easy 2800fps with the 100gn pills, but the proof will be in the pudding when comparing a 'preferred velocity to your sights.
Don't be surprised if you get a few 'sweet' spots along the way.