Hi Tom,
If using a Model "B" engine in a Model "A", the Model "B" oil pan needs to be modified by cutting off its flywheel housing. A Model "A" flywheel housing will bolt to the Model "B" engine without any modification to the housing. The photos show a Model "B" engine with a Model "A" flywheel housing, clutch and transmission going into my Victoria.
An alternative to using a relatively scarce Model "B" oil pan, is that a Model "A" pan can be modified to work. Reliefs need to hammered into the sides of the "A" pan to clear the connecting rod caps. This is easily done with a ball peen hammer. Also, the semicircle cutout in the back of the "A" pan needs to be trimmed to accommodate the larger Model "B" rear main bearing. I did this for the Model "B" engine that is in my Coupe.
In the case of my Victoria, there was zero gap at the tabs of the flywheel housing to the "B" block, so no shims were used. Also, the dust cover on the Model "A" flywheel housing may just touch the modified Model "B" oil pan, but it's not an interference, just a light contact.