i have a KLX 250 1978 in my garage. They made em from 76 onwards and are still in production.my 1978 model has steel tank and dual shocks ... not a monoshock like the 83 one pictured above. The steel tanks (ballbusters) were replaced with plastic around 81.
Aparently the early ones shook themselves to bits alot as they have no balancer in the engine. my model has a special bracket that bolts to the top of the head. after 82-3 they redesigned the engine based on the klr and incorporated a harmonic balancer type setup to reduce vibration.