Rubber boot

depending which shaft you have if it's 2.5 or 2.75 either the 2-40-1811 stub with the 2-3-8001 and the flange depends on the bolt circle which yours should be the 3102-36 flange and not the larger one found in the big bodies....

If your local driveline shop wasn't aware of that, bring that to them, that'll replace the entire head end with that stub, slip, 1310 joint and flange