That depends on how fussy you were with the brass. If it's only .032" thick, that really isn't much. I don't know if you angled the edge of the brass to match the angle of the back strap and fore strap, if you would even be able to tell.
A lot of the stock Ruger grips I've seen had a very small but discernible 90 degree angle between the face of the grip and the edge anyway.
It would be easier to fit the outer perimiter edge of the grip to the brass then shaving .032" off the back of the grip. Besides you wouldn't want to remove any more of that wood in back of the ferrules anyway. It's already pretty thin back there in stock Ruger grips anyway.
But I don't think this would even be worth messing around with unless you were also making a pair of custom grips as well and just fitted everything to the grip frame as needed.