Churchill: 54.25"
M10/Achilles: 69"
Ok 14.75" difference, over a foot!
374.65mm - 10.71mm in 1/35 that is a big plug to increase width and probably an extra road wheel for length, back in Black Prince territory.
Another option I just thought of is raise the hull and have sponsons over the tracks. Alternatively move the trunnions mounts forward, or the trunnions themselves back onto the breach with a counter weight on an integrated loading tray and have a counter balancing bustle.
Comet had a 64" turret ring, 247.65mm difference, 7.1mm in 1/35 still a lot to fudge. Messing with the hull height or trunnions looks the most promising.