I have read a bit about tandems but have only just got one myself. I read about screw down brakes or similar which the pilot would use on a descent. There's also talk of fitting a brake lever for the stoker to use on the additional rear but it can be a risk. I just looked at your link to more AMRs and there's the brake! Looks like an old Weinmann centre-pull brake or similar so maybe you could somehow dismantle one and attach it to the frame bosses. I've just nipped into my garage and checked one in my spares box and the pivot bolt centres are 65mm apart. Maybe the answer to the question.
I have read a bit about tandems but have only just got one myself. I read about screw down brakes or similar which the pilot would use on a descent. There's also talk of fitting a brake lever for the stoker to use on the additional rear but it can be a risk. I just looked at your link to more AMRs and there's the brake! Looks like an old Weinmann centre-pull brake or similar so maybe you could somehow dismantle one and attach it to the frame bosses. I've just nipped into my garage and checked one in my spares box and the pivot bolt centres are 65mm apart. Maybe the answer to the question.