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Can't comment much about the small block headers themselves and their fitment. I will say the big block headers suck fitment wise and I had to modify both headers extensively to fit my brother's 68, but while I was modifying the headers for clearance I also welded in O2 bungs. With that said the options for O2 bung placement aren't great but if I were to have to do it again here are some general thoughts.
1. Put the car on jack stands and start pulling the car apart, expect it to be down for a couple of weeks. You need to mock EVERYTHING up.
2. If you don't have a friend with a welder or can weld yourself your gonna need to source that.
3. O2 sensor placement. The short of it is that Holley (we'll use them as a source given they are the primary provider for aftermarket EFI) recommends the O2 sensors be installed at either a 10 o'clock or 2 o'clock position in the pipe for condensation reasons and any deviation from this will reduce sensor life. Additionally they want the sensor somewhere within 6-10 inches after the collector. You might have a hard time meeting that recommendation. https://documents.holley.com/199r11322r.pdf With that said you're not gonna get a proper O2 sensor placement on side pipes without it sticking out like a sore thumb or making some pretty significant modifications to the car. Just not gonna happen. With that said I've looked pretty extensively both on here and on the google machine and it appears that folks have reported several years of use with O2 sensors in less than idle locations without much issue. With that in mind YMMV and accept the fact that you might need to throw a couple of new O2 sensors in it every couple of years. In my case I welded the O2 bungs on at the 4:30 o'clock and 7:30 o'clock positions facing inboard. I'm also about 5-6 inches back from the flange of the collectors on the inside. I might have been able to go back 1/2" more but you have to leave room. The way I welded them in they clear the frame without risk of hitting the frame if the engine wraps alittle on the mounts and they hopefully will clear any obstructions provided the wires stay tucked up and out of the way. It's a compromise and we know what it is. I've also seen where guys put the sensors at the 12 o'clock position and run the wiring through the louvers. That seems kinda tacky to me but it is also another option.
4. You're asking about the steering box fitment. It's gonna be my guess nobody has piped up being very few folks have this combination and can't really comment on it. If that's the case you're kinda on your own. See item 2. You might need to clearance some pipes.
5. External Finish. if you are opting for the silver ceramic coating look it's gonna take a bit to do everything and it's gonna cost you alittle bit more for the look. I would strongly suggest that you purchase the black painted headers if you're gonna weld in O2 bungs and have them coated after all the work is done. My brother wanted the ceramic silver look. Jet Hot matches the Dougs coating very closely. Can't comment on how the Dougs ceramic vs the Jet Hot color match will continue or how well either will hold up over time though given it's only been a month or two.
As for your question about the inserts. They shouldn't be too bad to remove the muffler once you got to it. Basically how they are built is both ends of the pipe are flared alittle. One end is flared alittle larger than the other IE 4.25 inches wide vs 4 on the other end. Basically this is done so that the larger flange seats into the step on the side pipe that slides over the header. The narrower part slides down the rest of the pipe. Does it leak past the mufflers? Yep that's part of it unfortunately, but you wouldn't notice because it's leaking inside the side pipe itself. Now how hard will it be to swap out/pull the muffler. I'd be willing to bet getting that side pipe off the header collector after awhile will be a real bear.
Thanks for the great information. Just so I understand your O2 placement, you have them in the header or the side tubes? I guess I'll need to get them on the car to see where the best place is. Good to know many have run O2 sensors though without issue.
I am going with Doug's rather than Hookers because the black finish on Doug's is supposed to be high heat and they are also a bit cheaper. I want to keep them black. I guess the Hookers are just coated in a temporary paint that burns off. Anyone know how the Doug's black high temp paint holds up?
In our case they are in the header. You really don’t have the space in the side pipe for the O2 sensor because of how the muffler insert goes in. I suspect you’ll run into the same.
As far as how the black holds up, I suspect it doesn’t. I was able to grind it off pretty easy to weld etc.
Dougs Headers - Side Exhaust
