The first bike I ever bought in 1978 for $100 was an orange 1974 DT-100. It had, no lights, no back brakes, no auto lube, no speedometer, no seat latch (real fun over jumps as you tried to get the seat back down) and was fished out of a pond at one point (I kid you not).
Fast forward, I passed the old bike affliction on my son (owner of numerous CT-70, Z-50, ST-90, and XR-75s etc) we went to look at a 1972 red CT-70. While there I notice a bit of orange under a tarp. Asked the owner what's under the tarp, an old Yamaha enduro he says. Can we take a look? There it is, same as my first bike, same color, but everything is there and in almost pristine condition and 2100 original miles. Some negotiation and the DT-100 was on the way home with us. The Dt100 runs great and even auto lube works.  FYI the CT-70 was picked up 2 days later. 
What the bike needs is fork seals, tires, tubes, air filter, 1 rear spoke, new battery and a headlight bulb. I found everything but I want to go 6-volt LED on the headlight, but all I can find is 6 inches where these are 5 inches on this bike.
But the worst is I live in NY which requires a title on any vehicle pre-1972. Working on that as well.
If you read this far Thank You.
 

Congratulations on recapturing your first bike! This forum has a wealth of information, manuals in the tech section and numerous people who have in depth knowledge of these bikes.

Greetings from Tennessee. 
 One thing you need to do is change the brake shoes 50 yr old shoes can and will delaminate and will be dangerous I’ve had it happen to me 

Update
Changed both rear and front tires, tubes, rim liners and brakes (cleaned brake dust and lubed cables and pivot). New battery. New air filter. Replaced fork seals and boots. New spark plug. Will change oil when off stand. Have some 25/25 led light bulbs coming for the headlight and going to see if I can make them work by modifying the sealed beam. I am also looking at the posts on here on the topic. I am sure a 5 3/4headlight will fit on this but not ready to give up on original but also not paying $100 for an OEM 6-volt bulb.