I just put headers on my 78 G30 Ambulance with the 400ci engine.
I know that the 400ci is right in between big and small block so I am not sure if it will be the same for a 454 but its worth a shot
I ended up going the route of the Hedman headers, shorty plugs, and paint.
Anyway, I filmed the whole thing so if links work here you can see how I did it.
Its a 3 part video, I posted the last part here because its the most interesting but the others are out there if you need them
Hope someone finds this helpful!https://youtu.be/C2uqP5ij9kU
If the link doesn't work, just look for the YouTube channel: JeepSheepTV