Rear drum to disc conversion question, Do I need to do anything with the master cylinder? Options

[GriffGirl]

Someone told me he thought I will need to do something with/replace my master cylinder when I convert my rear drum brakes to disc brakes; something about the proportioning valve.

Here's what he said:

In regard to your brake swap, I could be wrong, but I'm almost positive that you'll need a different proportioning valve...When you do it, though, you should see about swapping the proportioning valve and
master cylinder (if it's different on the GTs)... Drum brake wheel cylinders and disc brake calipers use different amounts of fluid (typically) and if you swap from the former to the latter, your rear discs brakes won't be doing as much work as they should.

This is all greek to me. Help? Is this something I should look further in to?

[GriffGirl]

Okay, so just to be perfectly clear. And btw I probably should've mentioned - I don't have ABS.

I should replace the proportioning valve when I do the conversion.
What should I replace it with? Do I try to find a proportioning valve that is intended for the GT? Or is it something that is self-adjusting when replaced, effectively replacing it with the same thing that I have now, but new? Also, is this a part that is easy to find?

I do not need to replace the MC but it wouldn't hurt to do so.
My understanding is correct here, right? So if I were to replace the MC, would it be with a GT part or the ST part? And were I to replace the MC, is the P Valve automatically a part of that? I have NO idea what a proportioning valve is anyway. But I'm about to find out it seems. (Cool!)