1977 GS400 - how much crossover with 1981 GS450?

[gsdelta]

I'm trying to figure out how much crossover there is between a 1977 GS400 and a 1981 GS450. My owner's manual for the 81 450 doesn't cover the 400 back to 77, only 78. Is the 77 400 as good as identical to the 81 450 as far as maintenance, upkeep etc is concerned? I'd love to be a two bike garage, with one for riding while the other is being worked on (or one to keep nice and original while the other is turned into the cafe racer I've always wanted). But I don't necessarily want to learn a whole new bike all over again.

Will much of my skills and knowledge cross over, or are we essentially talking about two diverse bikes here?

[pete]

The major basics will be the same although the 400 will have points vs. electronic ignition on the 450.

The big differences will be details spec's and placement of mounts on the frame and so forth, but as far as maintanence goes, there should be many items in common as they're essentially the same basic motor.