It's been asked countless number of times.  The past week I have read 100's of forum posts and scoured wheels & tires sites for 10's or hours.  I have made up my mind; final and definitive... about 7 times!  Every time I think I got it; I read something else and have to start over.

I think I have it down path; but I'm left with one question; just to be sure!

Before the question; here is the necessary background info:

My current setup:

1. Stock suspension (old and tired leaf rear spring)
2. Replica rally wheels 15x8
3. Previous owner had spacers for the rear wheels.  When I replaced the rotors and did not put spacers back; the parking brake cable is now rubbing big time on tire and there is a little paint transfer from the caliper to the wheels.  This leads me to think that the backspacing of those replicated wheels is 4.5" but I have not measured it yet.
4. GTII 235/60R15 front
5. GTII 255/60R15 rear
6. Before removing the spacers; there was no rubbing and everything was fine.
7. Planning to replace leaf rear spring for fiberglass one (nothing else; just the spring) at the same time as the wheels.
   

74 Corvette Stock setup (as far as my research goes...):

1. Tire size: 225/GR70 x 15 (in today's measurement : 255/60R15)
2. Wheel size: 8x15
3. Bolt pattern: 5 bolts, 4.75
4. Offset Range: -13 to 10
5. Wheel Size Range: 15×6.5 to 20×8.5
6. Backspacing : 4"

What I want:

1. Torq Thrust 2.1 Polished 15x8 direct fit
2. Firestone Firehawk Indy 500 of 235/60R15 front & 255/60R15 rear
   

Here's my questions

1. I found the said Torq Thrust wheels in 15x8.  They have a 3.79" backspacing and -18mm offset.  Does that sound about right for what I'm looking for?  I want direct fit!
2. Any recommendation for the fiberglass spring; concerning rating and bolt length; given it's a big block and will have 255/60R15 as rear tires?
   

Thanks!

Correct backspacing for Corvette Ralleys is 4".  The wheels you mention would move tire out about 1/4", which will certainly clear inside, and with your tire size, will probably be fine on the outside.  My '71 has 255/60s on the rear, and they have plenty of clearance as long as you don't try to lower the car way below factory height.

I don't know about the Torq Thrusts, but many aftermarket wheels need the spacers to clear the calipers, so keep that in mind.