1968 A-body front disc conversion question.
 

Friends car has power 4 wheel drum that I am converting to front disc. Can I use the stock master or do I need a disc/drum master with a new proportioning valve?

The master is likely fine to continue to use, however you definitely want a disc/drum combination valve.

Thanks!

And if there is as Residual pressure Valve in the front it needs to be removed.

What might a Residual pressure valve look like?

Look in the master cylinder... factory drum/drum had check valves (item 26) in the outlets. Not sure about power drum but probably the same:

https://forums.maxperformanceinc.com...1&d=1780197405

Aftermarket check valves would be inline, could be anywhere. This is a typical example:

https://forums.maxperformanceinc.com...1&d=1780197834

Ive converted over by pulling the seat out of the front port where line threads in.
You can pull seat by tapping the cone shaped seat insert,thread a bolt in and yank seat
With needle nose pull the rubber check valve,reinsert the seat.

Good to know, thanks again.