Achipmunk, I used a 1986 set of Corvette headers. They are for a tuned port injected 350, but how they mount to the heads is the same as earlier 350's. In my case, I turned them up instead of pointing down because it is too difficult to clear everything pointing down. Too much junk down there and framerails so close, they don't give you a break. Even turning them up, I had to move over the steering box.
Yes, I too recall the post you refer to. And I moved over the steering wheel about an inch over at the firewall, but instead of heating up the firewall, I just cut it. I reasoned that because I will eventually convert over to a better wishbone front suspension and 4WD anyway, I will also, at that time, change the entire steering column and probably go with a Flaming River street rod column. So the firewall will change then anyway. And your estimates of an inch and a half for the steering box is accurate, although good luck actually getting it more than an inch and a quarter. You can do more, but will end up cutting up the inner fender for additional clearancing. I didn't want to do that if I am going to change the whole thing in the future anyway, which is why I ended up shaving the 3 bolt heads on the steering box for additional clearance.
I drove it around the cul-de-sac and turned the truck around and didn't notice any change in steering feel, nor the slightly altered angle of the steering wheel. It really is not noticeable.
One more comment. You mentioned using a 305 with a TH350 transmission. You have more freedom to modify the positioning of the V8 if you use an automatic transmission that does not require the shifter coming through the floor. Most people position their engines a few inches further forward when using an automatic so that they do not have to alter their firewalls. If you do this, you can use a standard stand-alone HEI no problem. Because I chose to keep mine manually shifted, I had to mount my engine further back to conform with the transmission's stock location, and that is why I had to modify my firewall.
