Well Paul you are not alone in not knowing how to do this and yes you can do this to your 8 71 , The hardest part was getting the old peddle out lol and of course the cost of the Items . It's pretty straight forward . Air to the peddle from the peddle a line back to the modulator tee off with each tee lenth the same lenth. I was able to position my modulator in line with my govornor and Ijust had to built a mounting plate to mount the modulator. the trans modulator was easy to remove and install the new one . On yours with the 4 speed all you need is the throttle modulator and air line and peddle . I got my peddle from Ron the Bus nut for 127.00 including shipping and you can scrounge around in some of those texas wrecking yard for a throttle modulator mostly on the pold cab over garbage trucks .
Andy Wright 68 Silver Eagle Model 5 8V92 #7481