727's /A904's are easy to rebuild at home if you have the patience and are meticulous with tolerances and posses a few special tools. (I.E. inch pound torque wrench) . If the clutches aren't burned up sounds like a valve body issue but willing to bet the trans pan and filter is going to show nothing but a layer of friction material. I just rebuilt a 727 for my 70 D200 with this same issue. I bet when he says "won't go over 30 mph" it is down hill with the rpms screaming from slippage.