To check out slippage. Take it for a ride to see how it acts.
Block all wheels, set the emerg. brake, start it up, hold the brake on, shift into 1st, speed up 1800 RPM, do you feel any torque, do the same in reverse, any torque, if so the convertor is good, the TC will rattle if it's coming apart inside. If you get a lot of slippage in either 1st or rev. then the tranny is shot. Kind of tough to diagnose if your not familar on how they act.
First of all, does he have a turbo, crossover exhaust pipes are a *****, you know, break the flange bolts, rusted nuts. Top 2 bolts on the tranny.
Without a turbo.
About the same as installing a rear main seal. Set all four wheels up on cement blocks or jack stands maybe both. Gives a little more room to work. Should be able to do the job in 12 Hrs. Hey I'm 82 and done it in 10 Hrs, no turbo tho. The only trouble you might run into is the cross member bolts on the frame. If you have an engine hoist, support the engine with that. A floor jack under the tranny, use a board on the jack so you don't bend the pan. Disconnect the drive shaft at the rear. Unbolt the shifting mechanism, disconnect the wiring, unbolt the dip stick, don't remove, oil runs out, 6 bolts to the engine, 2 nuts on the tranny mount, jack up the tranny remove the cross member, slide the tranny back, unbolt the TC 4 nuts. TC weigh's 55 lbs. dry, drain it if it has a plug.
When going back together, put the TC on the tranny, make sure the splines line up. When the TC is all the way on it should be 1/2" back from the tranny flange face. Two guys are best when moveing it back to the engine so the TC don't fall off, and to line up the bolts to fly wheel. Have fun.
Oh, and it's nice to have someone to hand you the wrenches.