There is a plate welded to the axle tube that has all the specs needed (see pic below). But yes your current axles are rated at 2600#. I have a '75 TW and I'm actually going through the axle process right now. I suggest searching the forums to gain the info you need to make an informed decision, but you can easily get overloaded with info. I've chosen to go with Dexter axles, and purchase them through Red Neck Trailer supply which both companies have been great to work with so far. Red Neck Trailer has a location <1 hour from where I live so I can pick the axles up in person which eliminates all shipping/freight charges. The only challenging part so far has been trying to get the order entry people at Dexter on the same page as the Engineering group, as far as what they will actually build (specifically whether or not a shock mount can be added to a #10 TorFlex axle). The answer is yes, as several other memebers here have gotten the shock mount bracket option from Dexter, however in the order entry software and the dealer books this option is not reflected as it seems to be unique just to AS axles, and thus causes (at least in my case) some confusion. After going rounds talking to different people at Dexter I finally got a Sales Engineer that could give me the axle part# that matches my dimensions and specs actually to what I needed. I would assume that that same axle part# would work for your application, however unless you go with Henschem original replacement axles, it will require you to drop at least one of your axles and perform two measurements 1) hub face to hub face, and 2) outside of mounting bracket to outside of mounting bracket. You will also need do a little home work on what specs/options you want/need to communicate to who ever you order from. Henschem is more convenient (no measurements, no drilling new mounting holes, no real decisions to make other than whether you want brakes added or not) but comes at a premium, other options are considerably cheaper (roughly half the price) but do require some additional effort on your part. I opted to go the route of Dexter and figure it will save me ~$800, which for me was too much to justify the convenience. Hopefully I feel the same way about the convenience after my axles are on and finsihed!
Feel free to PM me if you have more questions, as our applications are pretty much the same and I will share my experience in more detail. I hesitate posting any specifics right now as I'm currently going through the process, so I don't want to speculate on what will happen. I hope to finalize my order today and have new axles by next Friday, after that I will will be able to share more info.