This from the web :"Junior marines used to complete the first 12 weeks of training at Deal before moving to CTCRM , 229 ( Junior ) Troop were the last sometime in Summer 1977."
The HQ and training of the Band Service stayed until about 1989 I think.
The DI did seem a bit tubby, but I suspect others will be leaner! All have to pass a tough BFT every year. Some photos here:Lympstone
I have seen quite a few photos of recent senior NCO's and Officers that were "burly" but no doubt tough - the last 2 CGRM's - "Buster" Howes and Ed Davies were very strong looking. See the CTC RSM here also.