The OC used fork girders the same as the 600EWthrough E/F29; except the brake drum being on the opposite side as you noted. The same girders were also used on the TT, thought the brake anchorage and cable terminus are different again. Then when you get into the mid-thirties you cannot separate the girders and you are stuck with the central spring design. Not sure how authentic you are trying to get it. The only thing you need beware of are the forks used on the T6. These were a hold-over from the twin extension spring suspension of the 1929 600s, where as the S5/S6 got the new central compression spring forks (and different girders and link arrangement). However the T6 girders while looking identical to the OC/TT/600EW girders, are slightly longer to suit the change to welled rims and balloon tires. I think about 5/8" longer, if I remember correctly. Useful perhaps if you are making a mild trials version of the OC...
I think there is some info on the individual girder tubes floating about (bend info), but no general arrangement drawings that I know of.