Brake power or non power?

I would use a 7/8" or 15/16" bore MC, no larger. If you bleed well you should not have excessive pedal travel and an easier pedal force. An alum MC will save weight and look better, but all the ones I know are 2-bolt, so need a 4 to 2 bolt adapter ($30 ebay). Many use an ~85 Dodge truck one. I used a ~95 Breeze ABS MC (2 ports) on all my old Mopars. Don't go 99+, or often bubble flare ports, though you can actually form those easy (youtube).

The proportioning valve isn't affected by the MC or booster choice. All MC's I know of produce the same fluid pressure in the front and rear circuits. Your fixed prop valve is only proper for a certain combination of both front-rear brakes and tires. An adjustable prop valve is better if you tune it (wet parking lot) whenever conditions change (different tires, shoes or pad, ...). Cheap ones are $25 but you probably want the imbalance warning switch too, so ~$75. Your fixed one is probably close enough if you don't try drifting on mountain roads.