The four Tynes on a Merchantman seemed to have a higher frequency sound than those on the 44. The Merch props are smaller and probably operated at a higher RPM than the 16' props on the Canadair, which has a much deeper rumble from the more powerful prop/engine combination.
As for carrying RB211 engines, the problem surely is one of bulk, not weight. The heaviest RB211, (the 524-d4) weighs 4480kgs.
I am sure the Guppy can take 25tons out of EMA on an isa day.