Hi Gavin,
Thanks for pointing that out. I knew that US practice is 75% mbp, I forgot that British practice is 85%. Even though the GL has more TE than the 59, the 59 is a bigger engine and probably developed more horsepower. As you mentioned, the GL was a slogger, it had small drivers and was a low speed machine, compared to the GMAM (and its better looking sibling the GMA), Rhodesian 20th and East African 59th which were capable of passenger speeds. Too bad they never built the 61 class, that would have been spectacular.