What do you consider an upgrade?
I have a 1950 3100 "survivor" that has never been restored and was in regular use on a farm into the 1990s.
New tires and wheels of the correct original size made a big improvement in handling. Brand new Monroe shock absorbers (OE Spectrum and Gasmatic) made driving and overall handling suitable and safe for highway driving.
The front and rear leaf springs are original but not worn or sagging. Truck stays in a straight line over bumps and potholes at all speeds up to 65 (top). If your springs are worn out, new OEM style springs are available from Eaton-Detroit. Less expensive, original style springs are available from Rock Auto and other suppliers.
Replace what's worn out and broken and you won't need a so-called upgrade kit. These trucks handled just fine when new and still do when everything is in proper order.
To my knowledge there is no such thing as a bolt-on "upgrade kit".
