I read about the Skylab 1 mission in which SA-513 was used to lob the Skylab OWS into orbit. One source (http://forum.nasaspaceflight.com/index.php?topic=12519.20) gave some payload masses:
- Total mass to LEO = 147,531kg
- OWS mass = 88,474kg
- S-II dry mass = 36,697kg
- S-II/OWS interstage = 3453kg
- Payload shroud = 11,630kg
The extra 7,000+ kg is redisual S-II propellant, and also the S-IC/S-II interstage that failed to separate after being damaged by debris from the OWS.
Excluding the S-II and its roughly 3t of propellant, but including the 4.1t S-IC/S-II interstage, the potential for usable payload was between 107t and 108t.
This payload was delivered to 50 degrees inclination at 434km in altitude. So, what could it have thrown to 185km and 28.5 degrees? Studies (From 1965, I believe) on the very similar Saturn INT-21 concept give that launcher a maximum payload of 115.7t (not including S-II) to 185km and 34.5 degrees. The date of those studies means that this may not factor in late-model weight savings and engine upratings made to SA-513, which went up in 1973. Could it have lifted more than 115.7t?
Some other sources give the Skylab OWS mass as being 75,000kg or even around 77t. I'm not sure of what figures are best.
Also, how tall was the Skylab/Saturn V combo anyway? I've found 333.7ft, 341.0ft and 343.8ft, but can't verify any of them.