JIm,
If you want to run a rear disk set up you are going to have to use a period Air heart caliper and Master to be legal pre 75. I dont believe anything else was used and wouldnt fit properly anyway as you would be trying to fit a front disk from that period to a rear.
You can fit any standard yamaha rear wheel in those frames as i think they are the 19"/17" axles, so you can use any pre 75 YZ, MX or even the DT1 with the cush drive. Plenty of option there that bolt stright in.
For the front tripples what you need to fit is a TM 125/250 as they will fit straight in, Can use tapered bearings, Have the the longer Stem you need and also take your 35mm forks as is. (personally i dont feel the Aftermarket ones are legit in pre 75)
Use the TM front wheel set up as well ( so grab a complete TM front end and it will slot straight in and be Pre 75 legal.) its light and works - you want a small front end, not some mangy road peice of shit.
IF you feeling game run a spooler on the front, then you have a proper US bike if thats what your trying to copy.
here is your rear hub in a pre75 bike
