1978 390WR and OR

It seems to me that your original questions have been answered. A few comments about this above quote.

There is one club near you that would put a suggestion to stay home and do knitting if not up to it they most likely do put enduro riders through the nastiest stuff they have however often there is a diversion that puts A and b riders one way and C riders another. Most enduros have the A B riders go farther after the C go home. I remember one enduro where it turned out that last section or part of it was arrowed on foot not by riders like the rule book called for, that was in your general area as well. Over in this area by now all the allowable trails on public lands are pretty set in the special permit application process. The stuff on private land is often or in part trails used for their hare scramble (VHS if applicable but on Saturday) at some time in the past and most likely future. The closed course events that the VHS promoting clubs use are on private land for the most part. They do wave starts so stopper type obsticles would be excluded one would hope however they do go round and round on the same trail that in most cases has been used multiple times before. The terrain to a large degree is dependent on what the land owner has and allows the club to use. I am kind of amazed at how long of straights I have seen at the few ones I have been to. When I was active in promoting these type of events we would bump the trail into the woods and back onto the straight to keep the speeds down. Vintage here is 25 years or more as you most likely know.

Luckily for me I can opt-out early with the C-rider short course. Or, if desired C can go through the extreme section. Ahhhhhh, the advantages of being slow.

Today, I picked up the bike. It is not a 78. It is an MN frame making it a 1980. The tag on the engine is either missing or I cannot find it. So, I don't know if it is actually a 390. Is there any physical way to decipher a 390 from a 250? Without measuring the bore?

Well, I was just looking at pictures. Is it a safe to say that a 79 250 had 6 cooling fins on the cylinder and being mine has 9 fins, would make it a 390?

Yes