I looked at both the #311 and #336 Mallory distributors that are sitting here and they look identical to each other. The distributor caps and breaker points are also the same which seems to be a nuance between some of the other models of Mallory distributors.

Trev. I looked through my stash and find no fewer than (2) #311’s and (5) #336’s. They all have 14 tooth gears and use the standard Y hex shaft for the oil pump. For all intent and purposes, both the 311 and 336 models will fit and work in all 1955 and up Y engines. There are some subtle differences in the housings on all these distributors but that’s likely just a ‘year’ thing during the life of the production run for those distributors. There’s always a chance that there is a difference in the advance curves between the two models but the advance curves in those dizzys were easily changed once the breaker plate was removed so that shouldn’t be a big deal. I've no old Mallory catalogues to reference which might help to discern the actual differences between these two models.