I didn't spot your thread earlier. What a superb frame!
I think you're right that it's a 1995 frame. As far as the cable routing is concerned, by the 1996 model year, when V-brakes came on the market, the frames had a conventional V-stop on the top tube. They still had the two guides on the seat tube, one of which became redundant, except that some die-hards still stuck with cantis until Vs became universally accepted. And by 1998, they went to just the one guide, for the rear mech.
The purpose of the two hoop guides is just that - the upper one was a guide for the canti cable (that's all you need for cantis) and the lower one was for the rear mech. You don't really need any sheathing for it, although I'm sure it does no harm - but Voodoo brochures just show the cable going through the guide.
The solution you have adopted to convert the rear to Vs seems fine - it's a steel hoop after all, so no reason to suppose it might be worn away by the ferrule.
Although the post is a 27.0, the seat tube is a 28.6, so you may need a clamp for a 28.6. It's worth measuring the tube though, because I think it is a Tange Prestige Ultimate Superlight, which is quoted as a 28.6/29.3. That implies that it was externally butted at the top, so you may need a 30mm clamp. Anyway, I expect you'll make sure it's the same as the one you've snapped.
