Is there any way you can post some photos of the places where you are hitting your frame? That might help everyone and give you a few ideas.
Without seeing it, here are a few of my suggestions:
1. You might be able to raise the engine a little and/or drop the transmission some. *Usually* you try to have about a 4 degree tilt in your motor to the back of the firewall.
2. Take Nate's advice and try and re-bend the header. If you are not comfortable with doing that, find a local hot rod shop or old school exhaust shop. Most are more than happy to help out another hot rodder. Take photos so they can see what you have.
3. Depending on how much clearance you need, you can *slightly* dimple the header tubes if you need to. Yes, this will slow down your exhaust flow, increase backpressure and could reduce your horsepower, but if it is a slight dimple you will probably never notice it. However, keep in mind every dent adds up. If you have 1 5/8" primary tubes in your headers, a 1/2" dent could introduce a pretty major restriction.
4. I would avoid cutting the frame. Too much weight and torque in the front of the vehicle to be weakening the frame.
5. Finally, while you are at the hot rod shop just ask them what a custom made header would cost. You might be pleasantly surprised..
Good luck and keep us posted!
