Weimedog, seems to me you should first talk to someone at Hugh's Bultaco or one of the other Thumbs-up specialty shops. They can tell you exactly what needs doing and have the parts to make it happen. If you need a phone # or web site link, let me know. Still, the ol' Frontera was never a snappy motor as I recall. It was a grunty motor and actually quite competent as an enduro bike, once you took care of the minor nits and Spanish pot-metal (sorry) build quality.
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'81 490 Maico (King Kong!), 2000 CR250, 74-1/2 GP400 Maico, buncha street stuff