The original was a GR70-15. The Alpha sizes are no more, as they did not
always translate into the same size by manufacturers.  The Metric sizes are
not always the same, either, but they are closer to being the same.

Basically, equivalent tires are:

F70-15     215/70-15
F60-15     235/60-15

G70-15     225/70-15
G60-15     245/60-15

H70-15     235/70-15
H60-15     255/60-15

L70-15    255/70-15
L60-15    275/60-15

The 235/60-15 actually looks a bit small in the flared '73 to '77 fenders
and many run the 255/60-15.  The 235/60 looks better in the '68-'72.

The 235/60 can have minor rubbing on the front at full lock on the frame at
the steering box bolts and the idler arm bolts, so it is important to always
have the rounded carriage head bolt in here. Never replace with a regular
bolt and especially never have the threaded end to the outside.

The 255/60 can have the same rubbing, plus the back edge of the wheelwell
and the top of the inner lip. These were trimmed at the factory for the '78
and up with the 255/60-15 option.

The 255/60 can also rub on the emergency brake cable bracket on the trailing
arms on the rear, but the clearance can usually be gained with minor work
(some grinding, maybe move the bracket if excessive).  Be sure to fit a tire
to the wheel and check before driving out of the store with them on the car.

The 245/60 (the G60 equivalent) is a better fit from looks than the 235/60
and it less a problem from rubbing than the 255/60.  However, they are
usually hard to find.

Fitment is based on using factory rally wheels or factory aluminum wheels at
stock ride height. With age and mileage, the ride height can vary.  The
factory aluminum actually give a better fit of the 255/60 on the rear than
the rally wheels, so you may not have any issues on rear. You will still
have them on front.

I am currently running 235/60's with no rubbing, I guess I will stick with
that size.

Thanks

J