Roy,
Nice little project! You have two good location holes up front. I would use two measurements at the rear: from the valve cap receptacle on the head to the bottom of the oil tank, and from the hole center to the top of the side plate on the rear. This will give you a general location for the rear hole and provide the general position of the remaining front holes that will establish the rake.
With those two rear dimensions you should be able to finish up the front by welding the plates back on.
You can make the front plates (I used two pieces on mine because it was easier). You don't need the holes in the plates. You can weld up one side and then transfer the holes through the FT1/2 and drill them. The other side can be completed and you can drill the other way. The holes in the FT1/2 were said to be reamed initially by the Factory. You may want to drill slightly undersized holes and ream them at the end. If your careful, I don't think drilling or reaming will make a difference that will be noticable.
Once the front is good and it is within the window that the two rear dimensions allow, I would do roughly the same on the rear. I would fix one side, mark the hole and drill it. I would then restore the other side (minus the slotted washer) and transfer the hole through the FT3. Once the two holes are established, you could then weld on the slotted washers that would finish the rear mount and mill the holes to fit the washers.
You have to be a little careful with the FT/3's. Often they are drilled all the way through, but not to size. You might want to run a reamer through the middle. Many were only reamed at the ends because the through bolt was small diameter, it was the ends only that were sized to fit. It is worth checking them. You don't want to use an undersized rod to locate the mounting holes.
This UFM would be ideal for a racer because you could steepen the rake by lowering the rear hole while doing the restoration. If anyone is building a racer, it would be worth trading Roy a good UFM for his.
David