Frankly, in this day and age, with the costs you spent to build something like a 408, if this was me, I'd spend another couple hundred on a wideband O2 setup.
I bought one because I'm playing with EFI. (The original setup was narrowband) I would not be without it. My new EFI is native wideband, so an add-on is not needed.
You can "rig it" and pull it back out when done, and plug the bung on a carb'd engine.