There are alternatives to headers. There are a few styles of block hugger and shortie headers out there that may be easier to fit.
You could even run factory manifolds till the funds are available to build a set of custom headers. I'm sure you'll be able to pick up some factory manifolds for your XR8 motor for next to nothing.
I built a pair of these manifolds for my under body system. They started as a pair of factory corvette pressed steel exhaust manifolds that I picked up cheap on ebay. I cut them down and made and new collector and put in an O2 sensor bung. The bend runs in close to the block and bolts directly to the Cat converter. The whole thing is modular and easy to unbolt. Easy to build, compact and cheap.
Cheers