Common on BMX bikes and occasionally showing up on old mountain bikes. U-brakes and V-brake calipers are not interchangeable as the frame bosses are located differently.
The straddle cable is only 230mm long. If you need a longer straddle cable to get around your seat tube then you need to order an extra straddle cable. (Any standard MTB/BMX brake inner cable can also do the job).
Moruya Bicycles. ABN 27 559 728 517. 10 Ford St Moruya NSW 2537 Australia.