That's exactly the kind of wisdom I was hoping for! Thanks.
I should have described my situation for you all better so that you can even better help me along: I'm in auto service by trade and have had several Yamahas over the years, but nothing that needed reconditioning. When my father-in-law said he had some partially dissasembled bikes, engines, and parts laying around, showed me, then asked if I wanted them, I really didn't know what he had until I saw how iconic and currently popular these things were.
I quickly agreed to rescued the lot. He told me that I was welcome to put one together and sell it. I laughed and said, "If I put one of these things together, I ain't sellin' it. I'm ridin' it." I'd just sold my last bike to venture into a bigger one. However #2 came along right after the selling part. Delivery bills ate up the spare $ pretty quick. Thus, my plans to obtain the next bike were trumped by my baby's lust for organic formula.
So I'm willing and able to work through it piece by piece. But, all arrogance aside, the truth is that for all the bike service I've done, I've never ventured into something this dated and am not sure just how consuming and possible it will be to bring together everything I'll need to get a good runner -which is what I'm really after.
The vintage guys will probably want to smack me, but the engine currently on the frame is the '71 (XS1B) with no E-start. As such, my desire to remain lazy would be to put one of the later options on there with the E-start. Whichever one has the best parts availability would usually get my pick unless anyone thinks there's other things to think about with the other particular engine options I noted in my first post.
So any comments that you can add per the above would continue to be much appreciated!