Check out cyclechaos, they list all the CR80 models, and the differences for each year, and the serial numbers. I think the 1980 was the only year with the red engine.
I have:
1978 Suzuki TS100 (engine rebuilt, but needs CDI unit)
1972 Suzuki TS250 (running ok, but the carb is leaking, carb kit on the way in post)
1971 Yamaha DT1 250 (runs great, very good condition)
I've been a Yamaha guy since my first yammy 50 (in 1974), so the DT1 is now my pride and joy. I only bought it last week (on impulse), and I haven't even got it home yet. I'm counting the hours... :D