the best approach would be switched secondary tranformer taps, to limit excessive dissipation losses
The lm723 could be subbed by a precision reference too ...
For higher current(s) you need to recalculate the shunt resistor (R21) and the pseudo darlington circuit (T2 T3 ...)
But as mentioned the lm723 as a max vcc supply
There's a limit to the filtering capacitors (C10, C1,C2) check google for calculations, you need to add 0,1 uf 100v in parrallel of them
And you could add an anti reverse protection diode at the output terminals, it will help if you drive inductive loads
And yes this circuit may dissipate a lot, add temperature controlled fans, or a small fan controller circuit ??
You have many leaked Mastech (and the clones) psu's on the web, you can check how they implement the secondary xformer taps
Add multi turn pots instead of a single turn