The whole deal with a power supply is control systems engineering. A good power supply isn't in the first place about user interface, connectivity etc. It's all about the control loops for constant voltage and constant current. Although the basic principle is rather uncomplicated, finding the right implementation isn't. Its almost a quest of finding the right components, getting the loop to be stable in all circumstances, getting the CV and CC loops to have a very small cross-over region. Then try to make it fast while still maintaining stability. Oh wait, we want low noise too. Now add a bunch of protection circuitry and you've got a recipe on which each company creates their own solution.
Find amspire's topic on his power supply build in the projects subforum. That should give you an idea. He is going for his specific solution. Just copying his design but using another series transistor will most likely ruin your control loop stability.
The great thing about those HP 361x designs isn't in the components used, but how they got it all working together in a very great way. Present day of course the basic design has indeed matured. Still it requires a good understanding of the issues involved to achieve the same control loop stability, noise, speed etc.