Hydroboost conversion is what I had in mind when the time came.

https://www.powerbrakeservice.net/new-1967-1988-dodge-truck-d100-w100-hydroboost-brake-booster.html

Pretty sure GJ has done a similar conversion with factory parts and probably cheaper then the $450 pbs wants?

'68 Fury Convertible
'69 300 Convertible
'15 Durango 5.7 Hemi
'16 300 S Hemi