How many CURRENT owners of real '74 360 Duster 4 speed cars on here?

I still have my Duster. Just been busy with my Hemi car and now I've started working on the Charger.
I do have a question for the group and would like some feedback. How much if any modification is acceptable to everyone else? My idea is to pull out the perfectly fine 360 and install a warm 408 with an LD340 and headers, keep the 4 speed but upgrade wheels, brakes and suspension to do some more spirited driving and great burnouts. Since mine is a sunroof/space duster car, utilize the US car tool kit to stiffen it up as much as possible...or should it stay as stock as possible?
What stopped me from working on it is the massive hole in the roof. I cannot find the replacement gear and guide plate. Nobody is making them anymore.