Autolite 103's are great plugs. Copper is a much better conductor than platinum. Copper plugs oxidize more quickly than platinum so they need changed more frequently.
I prefer AR103 plugs which is the racing version of that plug. The AR's are automatically 1 heat range cooler and have the power tip. They are also copper which again is a good thing from a performance stand point.
Sorry I didn't realize you were still awaiting an answer. If you check out the link above you'll see on a heavily modded vehicle like yours .028 is recommended.
I run a gap of 0.030" with a different brand copper plug. (NGK TR6).
I originally had them gapped at 0.035", but it was blowing out the spark during boost (misfire only during boost). So its easy to tell if you dont have them gapped close enough.