Tire Sizes
 
"Sure a wider tire will give better traction; bigger contact patch to
transfer the power to the ground.

The 78 series tire has pretty much disappeared; the 75 series tire replaced it." I've seen '68-'72 A-bodies with 255/60R15 on the back & either 235 or
245/60R15 on the front. Looks great and a 255/60R15 is 27.04" tall which
is very close to your G78-14 at 27.06".

235/60R15 = 26.10"
245/60R15 = 26.60"
255/60R15 = 27.04"
G60-15 = 26.44"
H60-15 = 27.08"

235/60R15 = 26.10"
245/60R15 = 26.60"
255/60R15 = 27.04"

(235mm * .60) / 25.4mm per inch) * 2 + 15" = 26.10".



I've had the wheels off but I never checked the rim size. I thought Rally
wheels only came in 14 X 6. Do they come in 14 X 7?



Yup...

14x7 Rally II   4.75" B.C.   JH JJ JK JS KS  GM# 525709

69-75 Firebird
69-75 Grand Prix
73-75 Le Mans
77-79 Phoenix
   72 Tempest
75-77 Ventura II