Filister,
I'm not sure how much informational help you'll find here. Maybe someone who can help sort what can and can't be done will chime in.
It looks like it would be very easy to adapt a ford focus rotor and gm calipers to a drum brake hub. Anybody ever try this?
The Alpine was never equipped with front drum brakes, so unless someone in Europe or Australia has tried and is willing to contribute, you'll probably be on your own.
Looking to add series 3 brakes to my 57 Rapier.
You want to go to Series 3
Rapier Lockheed disk brakes and have the parts? Have you measured the diameters of those parts disks? Are they 10.8 diameter? I suspect you will only find replacements in the UK, if at all. The good news is if your current disks are in decent shape, they would probably last a good while.
You sure you don't want to go original with the drum brakes?
I did some searching and only found a listing for the later 10.3 inch disks, as you stated.
I'm about to do some wild guessing about stuff and parts I've never seen. The series 2 Rapier used some "massive" front drum brakes. Series 2 Rapier ended in 1959- Series 3 Rapier started in 1959. The Alpine didn't receive the new style rubber-bushed suspension until Series IV, late 1963. That is also around the time the Rapier changed to Series 4 with 13 inch wheels.
Here is where the guessing starts. I don't have a Rapier or Minx parts manual to check and compare specific parts.
Your s3 Rapier parts are of the "kingpin" style upright, as opposed to the later double ball joint upright and rubber bushed A-arm style. When the s4 Rapier began, it was mostly a make-do facelift because Rootes used the new body design for the Humber Sceptre. When Rootes decided to use 13 inch wheels on the Rapier ( think transplanted Alpine or Minx suspension parts ) the large Lockheed disks and calipers would not clear the 13 inch wheels. The Rapier required a new design upright for the Lockheed calipers to clear and for the double ball joint A-arm design. That makes my guess the new design upright lowered the caliper mounting for wheel clearance and required the smaller diameter disk because of the new mounting.
I tend to doubt the different style parts will play together with mix and match.
IF the Lockheed front hubs have a different wheel mount flange location than the Alpine unit, it
might be possible to mount that hub onto your current s3 Alpine spindles and disk. You would have to verify dimensions, bearings, and seals for both applications. If you try this route, be very careful as there were some major design changes in the Alpine units in this time frame and probably corresponding changes in the Rapier units as well.
Sorry for being long winded here without being very helpful. Most discussions about Rapiers here seem to want them as original as possible. You seem more of the "keep it on the road" mind set.
More questions, please ask. Plenty of people here with knowledge about things done, how they did it, and what to do differently if done again. It just wasn't on a Rapier.
Hope this was helpful,