That slider assembly looks very similar to the one I changed in my Saginaw. Don't believe that listing is correct, no Borg Warner 3 speeds were ever put in a H body. Whats funny is it even says on the box Borg Warner 4 speed....but still not a H body part.
Ok, that is the same part I changed, 1st and 2nd slider assembly. If you look close you will see the correct part number is 368051 which fits the Saginaw trans. They are expensive but not THAT expensive. I got a NOS one for under $100. I sent him a message through ebay....