http://idisk.mac.com/forever4/Public/pages/timingcovers.htm
Note that there is also a Model C timing cover. I will probably get in trouble for calling it a Model C instead of a Model 46 but I think everyone knows what I mean. The Model C had the generator mount further back to allow for the slope of the '33-'34 radiator and the bolt holes for the front motor mount were in a different location.
A Model B timing cover has an oval boss where the timing pin is and the pin is in a different location. You can't time a Model A if it has a B timing cover.