Have you actually measured the drop required, cheapest way is to file out the slot on a pair of std reach to lower the pads.
I don't know how much braking power you need but I have an old single pivot Shimano SLR caliper 47-57. The return spring isn't the strongest but it's functional and has a quick release lever. No AK nut and no pads but £5 will get it posted to you.
Have you actually measured the drop required, cheapest way is to file out the slot on a pair of std reach to lower the pads.
I don't know how much braking power you need but I have an old single pivot Shimano SLR caliper 47-57. The return spring isn't the strongest but it's functional and has a quick release lever. No AK nut and no pads but £5 will get it posted to you.