Sounds like it's getting confusing...
Answer = No. As Mike Mueller pointed out, not yet. Spindle size is different. Best bet is to research that 73 that has the suspension. You'll get a bolt-on solution at least for the fronts.
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73 911 should not have the "A" calipers, just the "M" calipers
Unless it's an S, which would have S-Calipers (the aluminum ones) not the "A-Calipers". A-Calipers did not arrive until 77-78 (I "think").
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I think it has the steel SC brakes
Possible, but more likely they are steel "M-Calipers" with the 3" spacing. Sombody may have updated it to the later style but that doesn't sound like something you would do to a rusting hulk.
RAR is correct:
S-Caliper = Aluminum.
A-Caliper = Steel version of the above.
Both have 3.5" spacing and do not fit on a 914 or standard early (911T) Boge front end. You must have either Koni or Bilstein struts in order to bolt these up.
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Does anything from the rear brakes/hubs work in a conversion?
Others are correct. The hubs will bolt up to 914-6 stub axles. Mittlemotor usually has these for $250-275 on eBay. $50 shipping. The emergency brake system will also work with little modification. Check my e-brake conversion thread in the "Classics". The rear calipers will then bolt on as well. This will allow (with the 911 front end) vented rotors all around. The entire package would get you a complete 911 system. At that point I would ditch the proportioning valve in favor of the "T" fitting. Other's can weigh in on adjustable valves etc.
I'm currently using:
Front -
Koni Struts
Koni Inserts
S-Calipers
Vented Drilled Brembos
Rear -
Koni Shocks
140lb Springs
Boxed Control Arms
911 Hand brake
911 Rear Caliper (911 fronts rub and need extensive modification to the nose)
911 Rear Rotor - Vented Drilled Brembos
"T" Valve in place of the proportioning valve.
This is the same "system" used on the 911RS and the 76 Turbo. I say "system" because I would "
really" encourage you to look at the system as a whole. There's been a tremendous amout of discussion regarding upgrading fronts (BMW, 911, etc...) and not rears. There's been a tremendous amount of discussion regarding vented rotors vs. solid etc.
I'm stupid so I left it up to the engineers at Porsche.
Hope that helps.