I've got a '77, this was the last year before the small cases came out. I own a few from '74-'81 and I think the '76/'77 are the best... long travel suspension, good power and great handling. The 74 1/2 has a good motor... no suspension, '78 are better suspension, good handling but they lack the power the 490 has.
In the end the '76/'77 is stuck in the middle and in the AHRMA class, it can be competitive. '75-'77 are in the same class hence the reason the '78 gets lost against the '80-'81 longer travel bikes.
Regarding reliabilty, I've only had 1 dnf in the last few years due to being a Maico. The only bikes that have faired better are my Husky's. Keep in the mind my bikes are stripped to the frame and FULLY rebuilt prior to racing... and keep in mind, it's a 30~yr. old bike!
Parts... all makes can be VERY expensive to replace parts, not always but if you build it correctly it's not cheap.
I rode Yamaha through the 70's so I can't relate to what they were like new.
If you don't buy in send me an email -
ernz@wt.net
PS>> Where in Texas?