There is only one magazine size for the CTR and your COAL will be limited by that (~2.95). Some guys have also fit AICS style mags into the CTR bottom metal but you are still inhibited by the COAL. So if you are running the shorter Shermans you will be ok with that.
Depending on which Sherman cartridge you want to run you will need a 'long action' bolt stop (or modify your current) and you will need to change your bottom metal from a CTR to the T3/T3X factory style(requiring a new stock) which with HCA mags you can run out to 3.38".
Talked to a guy at RedSnake Tactical and he said I could install the long action bottom metal in the CTR stock but it will have a gap on the sides is all, since the non-CTR bottom is slightly thinner than the CTR one.
West Desert Shooter has built a 7SAUM and made his action long with new bolt stop and then used a longer magazine but his was the Tikka T3 I believe. He has vidio on You Tube . KRG Bravo Make a stock that specifically uses CTR magazines.