Well - here's my current Ric lineup...
'64 4001S (not RM1999!) white (oversprayed), '72 fireglo 4001, '78 4001 blue, 2010 4003 jetglo, 2010 4003 mapleglo, 2013 4003 project, 4004 Laredo blue.
I don't get the weight thing - they seem no more or less heavy than anything else, except maybe my Rickenburger...
The Ric 4000 series evolved over the years, headstock, pickups, machines, bridge/tailpiece, pickups, construction, strap buttons, tone capacitors, truss rods, pickup position, serial number format, "glo" vs "glow", and so-on; the change to 4003 was associated with a truss-rod change, but all of the other changes are kind of blurred.
Interesting on the "glo"/"glow" naming, they seemed to drop the "w" in the mid 60's, as earlier catalogues had it.