This bike I'm currently working on has had a questionable radiator repair. I am guessing it is JB weld (epoxied), but has enough paint over it that it's hard to tell.
I have no interest in repairing almost 40 year old radiators. That seems like a never ending chase.
What options (other than custom made), are there for a new radiator?
A ZRX radiator is similar size (and DIRT CHEAP), but with the inlet/outlets on the sides I am wondering about hose clearance issues. Most modern radiators are cross flow so if this one is problematic, I expect most would be. Some ATV radiators are top/bottom flow, but most are going to be too small for a 1300.
Don't quote me on this, but I'm pretty sure I saw a photo somewhere of a KZ1300 fitted with a Kawasaki Vulcan radiator. It looked really good because the Vulcan radiator is a bit longer, but also a lot narrower so you saw more of the exhaust pipes.
There is a fella who frequents the Z1300 facebook page who has customised his 13 & fitted a Suzuki SV650 radiator. It does look good as it more or less is the same width of the frame down tubes, but my reservations for him that the radiator is from a model half the cubic capacity of the Z1300 & therefore of much less ability to dissipate the same amount of heat were answered with "it will be OK". I'm not so sure...