When you lower a car it can change the geometry of the suspension depending how you lowered it. SO the rims that fit a car that was lowered with drop spindles may not fit a car that was lowered with springs. Back spacing will be 4-1/2" on a car with drop spindles a little less with one dropped with springs. The other side to this is the these cars are no by any stretch of the imagination precision. What works on one with a 1/8" clearance will not fit another, Example: most 1st gens will fit a HEI disturber but I would guess about 15-20% will require the firewall to be "adjusted" to make it fit.

There are a lot of tools out there to help with rim selection but the reality is even the best car builder end up either testing fitting wheel and then modding them if needed or the get the wheels first and build around them. You best bet is to find people that have the same setup as you and use there setup as a starting point. You have a lot more luck searching build threads on any one of the dozens of Camaro sites then waiting for someone who has your same setup to find yours and decide to help. Try to avoid spacers if you can, while they are common here in the US they are illegal for road use in many countries due to safety factor. I would not be surprised is States start outlawing them.