Transmission fluid viscosity

Hello, my wife and i recently bought an 82 Blazer, ex-military( still in
camouflage paint scheme) and hauled our trailer to Spain...after a comedy of
errors trying to order an oil filter, im now being asked by the oil and
transmission change place to find out the viscosity needed for the
transmission fluid....I called the dealer i bought the truck from in the UK
and he said just standard ATF, with Bexron2 being the brand he uses. I
related this to the hombre at AutoPoint and he insisted that i needed the
viscosity.......so could someone please help me....asap please as they close
in 4 1/2 hrs and i've been waiting a week