Got the sc500 to run! I used the full setup from the regulator rectifier website. I only rode it up and down the street but it runs strong. it does want to die if you don’t blip it down to idle but I haven’t done anything with the carb yet. it does have a leaky crank seal, anyone got suggestions for parts on this thing?

Seals are likely just DT360A crank seals 1974 on, but I've not researched it yet, should be common.

Yes, I'm pretty sure the 1974 DT360 had the same seals as the SC500 and 73-74 MX360...  the bad part is that those seals were only used a couple years (only one year on the DT?) and are NLA from Yamaha...  they are not the same as later (75-on) DT models. 

(Seal OD is larger on the 74 DT360 than it was on the 75-on DT400 if I remember correctly...)

Bike Buzzard on ebay sometimes has single lip (SD) replacements but other sellers usually have the correct dual lip (SW) originals.  Can be pricey though. 

Not getting confused with the early 250 360 Mark? They're huge od. Now I've said that I'll do some research lol.
Ok i'll edit my mistakes. 38x62x10 right side. 30x62x10 left side.
Dt400 part number comes up 40x55x10 &--cant pin down the dimension of the left side probably 30x55, i'll find it lol

 

I'm pretty sure the first of the 1973 "new design" MX 250/360 engines (and the detuned 1974 only DT250/360 based on that engine) had oddball crank seals that were different from the 75 DT250/400?

I'm trying t save face but failing dismaly to link bike buzzard on ebay so type it 174759608323 Ebay
Yamaha LH Engine 55mm O.D. Crank Seal Replaces 93103-30150-00 NEW!
They have untold stuff down the page. Sorry just copying random stuff to see if itll post.
A new LEFT SIDE crankshaft / Engine seal for the 1975 - Later Older Yamaha DT250 400 #560 & other Engine Models....sold each....the seals you are replacing this with should be around 30mm x 55mm in size......
I'm learning every day.

I sent you a PM on someone that has the original seals available.

I am running a DT250/360 VAPE system on my MX360. Works great. Just make sure the BTDC is very close to 2.5mm. Starts 1st kick almost every time. Throttle closed, choke on until the beast warms up a little.