A real 1 of 586, 360, 4 speed Duster? You've got more guts than I do.
I struggle to cut the floor out of mine for a 5 or 6 speed, and you've gone exponentially beyond that. Truthfully, it's one of the things I don't like about my car, wish it was a /6 or 318 car so I wouldn't struggle so much to modify it.
Looks like you are doing a good job melding the two.