Hey Mike/Gary...
Gary has done a fine job describing the relative difference in sound between a 5 and a 61/2 deep drum... not really much to add there! In the case of the Dynasonic:
A "Big R" COB Dynasonic in the 61/2X14 size would go very well with your 70's "Londoner V" kit. That kit, is in essence, Rogers 5 piece Rock and Roll model, which would be great with the deeper Dynasonic. However... ( isn't there always a however?! ) ...
The 61/2X14 Dynasonic is going to be harder to find... even in the "Big R" series, and they did build MORE of these during the 70's. They are out there though. I've seen more than a few come up on eBay... and ... a lot of times they aren't paid all that much attention. So, at times, you can walk off with one and not be in too much pain! :-)
Tommyp