Does anyone have a suggestion on how to change the lousy 3-speed standard shift transmission to a 4-speed or 5-speed, please?!  

On what?  

..on a 1955 Dodge 1.5 ton  chassis parcel delivery van (Railway Express Agency).  Again, the original transmission is a standard 3-speed, geared for door-to-door delivery.  I want to install a better 4-speed or 5-speed transmission for better driveability.  Engine is a flathead-6.  

Gene,

That one's an oddball for sure. Find out what the rearend gearing is. Chances are its real low. It would be easier to change the final gearing than adapt another trans. Or you could swap in a later engine with an OD type 4spd auto or 5-speed stick. This brings us back to the final drive gearing, and if its real low like a 4 or 5 something to 1 you'll still need higher gears. Another option is a Gearvendors overdrive, they are in El Cajon, CA. see if they can help.  

I'm trying to avoid messing with the rear end, or replacing the engine which I just rebuilt, or installing overdrive units.  I really just want to swap out the 3-speed standard for a 4- or 5-speed standard.  Doesn't somebody out there know if Dodge (or Borg Warner) made interchangeable transmissions for 1950's trucks?  I've seen a few on e-Bay, but they all have different mounting ear spacing.  Does somebody on the list have experience with swapping those out/modifying clutch housings, etc?  Thank you, Gene.  

Dear Super-gene
New here myself.  You might try pilot house forum.  that is the dodge site that deals with the old flatheads and what others have done to get them the way they like'em.  I am looking for a 3 speed floor shift myself to go in behind the old flathead six.
Tinlizzy  

Gene any luck on finding a solution to your swap yet?