Whats the distance from base to center of lens on 7D?

[Ted Ramasola]

I'll be modifying my rails to fit the DSLRs, I want to know if the distance from bottom to center of lens of the eos line is the same beetween diff models.

Say I have an old 300D, can i use it as a stand-in for the 7D to configure baseplate height for the 7D?

We're nikon users in the studio so not so familiar with canon.

Ted