I have a distant memory of doing a run-up (on all 4) on a cold night-shift at LHR around 1975 following an engine change on a Merchantman (a good exercise in putting one's faith in brakes and chocks
).
If the main deck floor had been lowered during the conversion, presumably that would have resulted in there being a step up into the flight deck. I don't recollect there being one (I'd probably have tripped up over it), but I may be mistaken about that.