Looking for more braking power.... The 14x6s with decent tires aren't locking up with the current brakes.
Two part answer.
a.
Not locking up. Assume this also means not stopping hard, which is why you asked about upgrades. On a wet surface or even a dry surface, slamming the brake pedal should result in lock up of at least one, preferably two or all four wheels. If not, something is wrong, and some investigation will be required.
->As the car is new to you, look at all the pads and shoes - write down or photograph their condition and if readable, the edge code.
->Bleed the brakes, all four corners. This will do several things. One is that it will provide clues about the condition of the hydraulic system. If there's a bad hose or blockage it won't bleed. If there's a ton of rust, a piston or cylinder may be hanging up. Another is that the brake fluid absorbs moisture, so it should be changed regularly (I do every Spring) and this flushes out the absorbed moisture along with any rust accumulation. In my experience, Valvoline's synthetic DOT 3/4 has been the best of the normal (street use) glycol based brake fluids. With it, I seem to get the the least moisture and rust in fluid of the ones I've tried including Castol's LMA (low moisture absorbing).
b.
Upgrades Yes there
are differences in brake material. There are also trade-offs related to how they achieve their grip. Assuming stock brakes for '72, the pads will be D11 and the shoes 311.
For the D11 pads and 311 shoes, you will probably get higher gripping linings from a high performance manufacturer. Amongst most part store brands the
friction rating of the edge code can be used as a rough guide as to which ones will grip better cold and hot. As a guidepost, the Mopar factory replacment pads made by Cycleweld had a friction rating of FF. Accept nothing less for the front pads.
Amongst the more race oriented manufacturers there are a fair number that offer D11 street pads, more limited for the shoes.
Some to consider:
Porterfield RS4 I've been using on both pads and shoes for about a year, 7,000 miles. So far, very good and similar feel under all street conditions. They can arc the shoes to your drum diameter.
EBC Red Stuff Several people on FABO wrote the stopping (presumably grip) with "Red Stuff" pads is very good; also fairly dusty.
Hawk HPSRochester Brake and Clutch Not a manufacturer but a shop that can provide a wide range of linings to whatever pad or shoe. Can arc the shoes the drum diameter. Tomquad uses them for his street/track day cars.