407c, 507c and 508T all have the same RMR footprint
The 407k, 507k are smaller.
There is also the mailbox 509T which I believe has an adapter to run on RMR footprint for those who want a fully enclosed optic.
And as the poster above mentioned the T models are titanium housings. Electrically the 507c and 508T are identical.
407c and 507c are identical with the exception that the 407c has the 2moa dot only vs the multi dot configuration of the 507c. But someone showed a video if you removed the battery on the 407c and ran solar only that it has the circle dot reticle....must just be a internal programming thing to make more money by making a simple change on their end.
The V2 models with from the bottom mount 2032 battery to the side mount 1612 or something around there sized battery. The non V2 actually has a longer battery life, but you do have to remove the optic to replace. where the V2 is exterior so no return to zero issues.