As for the EGR, many perceive its presence as "evil performance robber", BUT that only happens when the valve works, no other time. Therefore, just deactivating it is all that's really needed, which can be as easy as blocking the vacuum going to it. DO, though, remove and clean the valve's mating surface with the intake, for good measure, so that when no vac gets to the valve, no EGR happens.
As for the part number on the factory block-off plate, I suspect that those are now long-gone, just as similar ones from GM most probably are. Having been OEM back in the 1980s for HD truck chassis models, originally. As they were also mentioned in some OEM HP parts books, they got to live a few years longer in the warehouses, but when sales stop, as with any other part, when inventories fall below a particular level and are sold out, no more are re-stocked snf the part number is discontinued. Just the realities of the parts situation. But, if desired, it should be easy to fab one using the EGR gasket as a guide. Still, though, much easier to just kill the vac to the valve.
As to a new valley pan gasket to block the heat crossover to the intake manifold, which ALSO makes the OEM choke not get any heat to open, which then required a full-electric choke for the carb (rather than the OEM electric-assist choke) . . . I had a friend who did this on his '79 Corvette and after he got the carb recalibreated a bit, he had no real issues with cold-start driveability. At the time, it seemed that our more temperate climate in N TX helped a bit, but he also knew how to change the starting technique to compensate too, if needed. NOR did it really make the car more powerful, either!
When I installed '86 Corvette aluminum heads on my '77 Camaro 350, with no factory heat crossover passage (as manhy replacement aftermarket aluminum heads are very similar, due to fuel injection), I noticed a few things. One was that the heater got hotter quicker. The other was that I had to tweak the elec choke adjustment to get things to work right on a full cold-start situation (on an OEM-replacement Holley 4175 with full-electric choke). With no little bit of exhaust heat, it was definitely a bit more cold natured in cooler weather, as our winters have become more intense in the last 20 years. Compound this situation for a B/RB Chrysler V-8, where the intake manifold is in "open air" rather than sealing the top side of the motor. Other than heat convection from the cyl heads, the other warming air will come from air which has been heated by the radiator, which can take a good bit of run time to happen.
Therefore, any recommendation to block the heat crossover passage should be tempered to the location of the vehicle in question, to me. Plus knowing how such a change could otherwise impact cold-start performance, too. As I now know how such a change really can change things in DFW, TX, in more recent times compared to earlier times (due to seemingly yearly changes in climate), being in a colder NY climate (colder longer times) might really need the exhasut heat in the intake mainfold plenum for a better driving experience. But in Brownsville, TX or San Diego, CA, it might not be that big of a deal. Many people who are more used to dealing with fuel injection engines might not desire (OR learn or understand) how to deal with non-efi engines, whicih might lead to a "I don't like this" orientation toward older vehicles. Which might lead to a non-blanket recommendation of blocking the intake manifold heat passage on engines, especially for vehicles driven more "daily" than not. FWIW
I'm glad to know about the "factory information" on the conversion, especially as most of the affected vehicles are now in the "antique" realm of things and might not be subject to yearly emissions testing. Over the years, Chrysler used several general model-year specific color combinations on spark plug wires, but all usually had the normal resistance conductor in them. So those changes were more cosmetic than otherwise. I do concur that a newer, lower-resistance conductor might be better than the carbon-core conductor. But even then, there are some which also tend to discredit the newer conductors as "marketing hype", by observation. I have the old Borg-Warner (now "BWD" Cool-Wire, monel-wound conductor, lower resistance spaerk plug wires on every car I now have. Long term durability is great. Don't necessarily have to spend big-bucks to get that same conductor in a spark plug wire, by observation.
Enjoy!
CBODY67