Got a chance to review some of your measurements. Looks like an Alko set up at 29.5 - 33 - 29.5 hanger spacing. Alko calls out a 26" spring but it is actually 26.25. the spring length assumes use of equalizers and shackle links that are the same dimension as Alko shows in their attaching hardware kits.
Found a PDF brochure of your year trailer - it says 6k axles are standard. The heaviest spring I would use is a 3200.
Have you weighted the trailer to ensure it isn't overloaded? Might be a good item to verify axle size. Alko axles have a metal id band, around axle, near right hand brake mount flange. Dexter axles have decal stuck on the axle.