5.9L Magnum questions

If you have the flex plate that was on the 5.9, you will need to use that back because it has balance weights on it. Three bolt holes for the converter will line up and one will be about a quarter hole off. Rat it out to fit with a round file or a die grinder and you're good. You probably know, but 5.9 external balance is different than LA 360 external balance, even though both are 360's. Others have tried to use LA 360 balancers and weighted converters on 5.9 Magnums and then wondered why their motors sh sh sh shook! lol. As far as exhaust, there are some Magnum manifolds that breath better than the early A specific ones like you have. I think they actually came on Dakota R/T's like the truck your motor came from. you may have to fiddle with them on the drivers side by cutting the collar back on the steering column. They do get close to the firewall in pics that I have seen, so you may have to add insulation. Doug's D450's fit pretty well. Sounds like you have a good plan, plus @TrailBeast offered excellent advice based on hands on experience! Good luck with the build.