Need to see actual pics of the interference. Kevin is correct, many aftermarket support frames do not have any "crossmember." But I would like to see what crossmember you are talking about. If it is what I think it is, remove it. If it what I think it is, it is not necessary for structural strength, so leave it removed. I would refer to it as a gusset or a bracket for something.
Fan:
1. I assume no original mechanical fan, just electric?
2. A SBC should cool just fine, no need to go overboard.
3. Electric fan should be mounted per mfg instructions.
4. Normal installation of a stock mechanical fan and shroud is fan blade about 1" from RAD and blade half in shroud and half out.
5. Fans are only for low idle RPM's..........under 30MPH. Ram air cools otherwise. A shroud and electrical fan could possibly block/decrease ram air flow in some DIY efforts.
6. The only reason I see for electric fans is lack of space or as a band aid for overheating. A mechanical fan works otherwise and is fail proof.
