Lionel 6-18404 San Francisco Trolley

Yes, the 18404 trolley has a pullmor motor.
I've had them on my bench, and I just checked the Modern era service manual. It's in supplement 10.  This trolley's construction is very similar to the Postwar Lionel #60 trolley. They are designed to run slowly.
This is mentioned in the Postwar Lionel service manual.
Here is the first page of the documentation, which Olsen's has made available on the web: #60 Trolley.

If I remember correctly, the modern-era Pullmor-motored Trolleys (there were three -- 6-8690, 6-18404 and 6-18419) were geared differently from their postwar #60 predecessor, leading them to have a more "spirited" (aka fast) speed.

I don't know what the OP is up to, but I'm not aware of anything that would have much more in the way of low speed control than the can-motored version he already has.

TRW

I can attest that Lionel current Birney low speed control is not very good.  It will run slower but when it bumps it doesn't have enough inertia to throw the switch into reverse and it stalls.  I thought maybe the San Francisco Birney is based on the gang car since the pole rotates on bump.  The gang car runs slow but mine has a lot of friction in the mechanism and needs a mini-crash to reverse.