I would like to put 2" dropped spindles on the front of my 39 Chevy Master 85 sedan, the previous owner added front disc brakes, and later model spindles but I don't know the year, is there a number on the spindles that would identify the year ? I see spindles listed as 1964-1974 online

Thanks

Your best bet is to determine who supplied the disc brake kit and the spindles. Even though there might be a casting or forging number on the spindle the same raw part can be made into many different machined parts.

The safest and simplest approach would be to buy a compete dropped spindle and disc brake set-up from a reputable hot rod supplier. If you mix and match parts any problems are yours to solve.

A riskier approach would be to make the needed conversion parts and mount the axle above the front leaf springs. There are a lot of unknowns and potential problems such as steering geometry in this solution.

I would be locating a dropped spindle and brake conversion kit from the same supplier that way everything is made to fit together easily. I would not be mounting the springs under the axle as there will not be any location items which will cause worse steering issues than the dropped spindles will cause.
Tony