My suggestion is that you take the car and the wheels into the tire store and tell them you want the biggest 60 series tires that will fit without rubbing. Go with the same tire on all 4 corners. The limiting factor will be how much tire you can get on the front without hitting the fenders.
My tire shop ended up putting 205 60 15's on my '65 (with 15X7 wheels), but it is lowered in front and the backspacing may be somewhat different than your wheels. Perhaps you could get a bit more (215 60 15 for instance). ANYWAY...if you let them tell you what will fit, they'll be somewhat responsible if it doesn't work out. If you tell them what to do and there is a problem...it'll be your baby.
I run 15x7 225/60 up front, 15x8 235/60 out back on a 68 coupe, I like the look.
That table that was posted earlier bugs me a little......on the 67-70 chart it shows 15x7 with 4.25" BS running a 225/60, but goes on to show a 15x8 with 4.5" BS also running a 225/60. I think a 225 on an 8" wheel looks kind of weak, you need a 235 to really get the effect of running big meats. 245 is also an option. I ran 15x8 all around with 235/60 for a while.......slight rubbing with rolled fenders at the front, no probs in the rear. I lived with it for a few years until I cut through the fronts, then I could justify two new 15x7's for the front with 225/60's.......I've experimented on the coupe and a 68 convertible I used to own and found this to be my favorite setup. Hope that this, combined with everybody elses opinions helps yuo to make an informed choice.
Correctomundo......point being, however, the fitment chart is just a guide and clearly there are other combo's that will and do fit, and (depending upon the eye of the beholder) look more attractive/aggressive/insertothercooladjectiveshere!
However, my original point was that 8" wheel just aint right with a 225/60. Go with a 7" in front and reduce the increased bumpsteer and unsprung weight associated with the 8" wheel (and you WILL have more bumpsteer - I had a 68 vert and a 68 coupe at the same time, one with 7" and one with 8" in front and there was a difference), and save the 8" for out the back if you want more meat. Additionally, on a stock suspension setup the clearance between the inside wheel lip and the upper control arm is so close that a wheel balancing weight won't fit.....I had to run my 8" up front without balancing weights.
Anyway, more meat on the ground, like more ponies under the hood, is what it's all about.