Re: time for tires and rims!
Those 215/60R15's should fit fine up front, but I'd personally consider moving to 225/60R15 just to get a little taller tire (25.6" tall vs 25.2", not a major difference). I'm pretty sure those 225's should fit a '67 fine as well, but you might want to double check.
For the rear, I'd go with 15x8 w/ 4.5" backspace. The 5" backspace would move the wheel inboard more and it might be a bit close to the inner wheelhouse (backspace is the distance from the inside lip of the wheel to the mounting face). The 8" wide on 4.5" BS works fine on a '69, pretty much centers the wheel in the wheel-well. I think the outer fenders are a little tighter on the 67/68, but I'd still be concerned with inner w/w clearance with 5" BS on an 8" wheel.
The 275/50-15 tires might be tight in the back, but the overall size (26.1") seems about right. I'd be tempted to try them as a track tire at least, but I'd be pretty worried about treadwear if you drive the thing much as a daily driver. The drag radials also have a much squishier sidewall, which helps forward bite, but can make the car feel weird in corners. Since I don't do drag racing, I'm not a good judge of whether it's worth it or not.
If you DO go with the Radial T/A's out back instead of the drag radials, you're gonna be stuck with a narrower tire (or a really tall tire). I'd think a 255/60R15 would be a decent compromise.
Tire choices for 16" wheels are pretty slim, so unless you really HAVE to have them, I'd stick with 15's or step up to 17's.
Just my opinions...