I agree with Yoda in that it would be best to upgrade the brakes and suspension first.it's alot more fun to have a good handling/braking bike that may be alittle slow than a fast wobble that scares you!
With alittle research I was able to find the right capacitor to substitute for the battery of my 91dr350.After starting the bike the lights and blinkers worked better than with aweak battery.All a battery eliminator is is a capacitor.
I just got a 78dt400 U.S. model and found the Clymer book #m412 to have alot of info.It coversDT and MX singles 1977-1983.I was in France last year to visit my brother who lives outside of Paris and rented bikes and had a blast!!