If you remove the stock steering box, which causes most of the problems, there are a number of solutions. If you leave your stock steering box out there, you can shim it out a bit, up to about 2.5" away from the exhaust ports of a small block Chevy, and also replace the 3 thick-headed bolts for a little additional clearance, but that still doesn't give you a lot of options.
Sanderson QP1000 cast steel headers are the tightest bend radius out of the heads that you can get, and although they probably don't flow as well as long-tube headers. They will flow a lot better than stock iron manifolds. The other option that seems to work with the stock steering box shimmed over are Corvette-type ramshorn manifolds. Those stick out a couple of inches but are supposed to clear.
There is one other cast iron header that is supposed to flow quite well, and that's the Tru-Ram headers from Speedway motors. However, they stick out 3.25" from the heads, which still won't clear a shimmed-over OEM steering box. And if you're gonna remove the steering box to use something else, then you have room for some types of tube headers.
The engine sits very low in the engine bay when you convert to a V8. So low that the frame rails just about come up to the bottom of the exhaust ports. However, there are some headers made for fat-fendered hotrods that have the primary tubes come straight out to clear the framerails and then use the front fenders for additional clearance. If you were to remove the steering box, those become an option.
I have heard of some people modifying tubular headers to clear the stock steering box, and I was initially going to do that too, but then they weren't deep enough to clear the transmission crossmember. So in my case, I think I will go with the Sanderson cast headers, deal with slightly less than ideal flow, but still have decent flow. I'll see how it feels and report back on it this summer.
