A voice with sad experience here: Might be more cost-effective to sell the SR and buy a used road bike set up the way you want.

I had a Univega Gran Rally (great bike) that I fitted a 700c wheelset to. Used an 8 speed 12-28 cassette. Spreading the frame the few mm was literally done by hand. Aligned the dropouts vertically with a 12' Crescent wrench. Kept the down tube shifters. No need to change anything beyond that. Could use the same Shimano 600 derailleurs and crankset.

I've sunk too much money into projects that ended up being up being almost as good as a decent used bike that I could have bought for less.