front disks stockish upgrade on 73 javelin

I got KH rotors on Amazon,
 waited for a price drop, and paid $74.10 each.

Currently they are just over $100, and only 1 available.

https://www.amazon.com/gp/product/B001DAEE9O/


I'd suggest you put them in an Amazon cart/save for later, and watch to see if there's another price drop.

Anything around $90 each is a pretty good deal.


If this were 25 years ago,
 I'd suggest grabbing everything from  the spindles out from a later model Concord at your local junkyard,
 but I think those days are over.

The later model stuff used to be cheaper for replacement parts,
 but I don't know how much cheaper they are these days.


These are the Kelsey Hayes brake pads I bought to go with the rotors:

https://www.amazon.com/gp/product/B000C702XG

there are probably better, and or cheaper options,
 but they looked good for around $35.

I'm still looking to get started on my brake rebuild (among many other jobs),
 so I can't speak to the quality of the parts, other than knowing Raybestos was a good brand for replacement brake parts in the past.



For rear discs,
 anything is possible with a little time and fabrication,
 I know Jeep ZJ (Grand Cherokee) disc backing plates have been redrilled to fit axles other than the D35/44's they came on,
 but just be aware that your drum backing plate is also your bearing retainer plate, holding your shafts in.

 And the stock axleshaft/wheel bearings are preloaded as a set against each other,
so whatever you do to modify or replace the factory rear brake setup has to be thought out to both retain the axleshaft bearings, and still allow them to be preloaded against the opposite axle shaft too.

There are other options like replacing the factory tapered wheel bearings with a type that doesn't require preloading,
 but there is an expense and compromises with going that route too.

If you are happy with your gear ratio,
I would suggest rebuilding the stock drum setup out back,
 retorquing your axle shafts and calling it good.

If you're not happy with your gear ratio (especially once you add a 5speed),
 start junkyard axle shopping.
 No sense changing gears, and brakes, while dealing with bearing preload and 2 piece axle shafts if you're on a budget and originality isn't a priority.

Tires?

Tires are funny now,
 Plain jane BFG 235/60-15's (a decent size that fits front and rear on most Humpsters) cost more than Hi Performance 255/40-17's from the same company.

Most of the time, 17's are the new cheapest performance size tire to buy now.

15's still look ride and fit great on our cars,
 just know you'll pay premium tire prices for them, and not be getting premium tire performance (for the most part).

Good luck

If you're not worried about a park brake rear disks are cheap and easy. Cut the drum backing plate down to just the bearing retaining part. You can get weld-on caliper brackets from Speedway Motors for standard GM calipers. You can use those with park brake built in or go cheap and forget the park brake. You can add a manual go-cart caliper later for a park brake. Won't do much as an emergency brake, but will keep the car from rolling off when parked. One note on the GM calipers (or any others) with built-in park capability -- you have to use the park brake some! It has a threaded stud that clamps down and is self-adjusting. If you don't use it some the park mechanism won't clamp down hard enough to hold the car. When changing pads you have to screw the stud out to move the piston back.

I don't have a park brake on my car, but it's an automatic. I keep a set of steel chocks in the back just in case I have to park on a steep incline or have some kind of brake issue and need to leave the car somewhere. Been carrying them for 14 years now and can't recall using them at all, but they are there just in case...  Hmmmm...  did use them once when changing a flat tire on the Interstate shoulder near Atlanta...

These work just as good for a park brake, at 1/3 the price.
http://www.gopowersports.com/manual-brake-caliper/
Adjust to thickness of caliper by using spacers in the body. There is a floating mount available also -- scroll to bottom of page.