I've been using a 488RC2 head on Manfrotto 055ProB legs for a number of years and I want to upgrade the head in order to use an L bracket. The pan base for the head and the mount base on the tripod are the same size.
I'd like to use a Markins head but the bases are: Q10-62mm and Q20-68mm. The base on my tripod is only 60mm.
Does anyone see an issue with this 'overhang' Eventually I will upgrade the tripod as well but I don't want to do both upgrades at once.
The 'overhang' which you mentioned is a non-issue.
I did the ballhead change to Markins M10-Q (arca-swiss standard) a few years ago and I won't be going back to the Manfrotto ballhead anymore. My tripod is still the old Manfrotto 190ProB which refuses to go quietly into the night.

