@ Ceasar 222
I had an SR2 turning a generator that was very dirty when first acquired. Removing the tin from the cylinders was sufficient access to get them relatively clean by stuffing a rag between the fins. If you want really clean, a blast with a pressure washer (all vulnerable bits protected) or for spotlessly cleaned, a disassemble and hot tank immersion would work.
BTW, I also had a marine SR2 in a boat about 50 years ago.......what a great engine. Noisy, but absolutely reliable......and the exhaust heat could be directed into the cockpit for warm feet.
Cheers
Hugh