Dave,
I talked my friend with a 440-6pk, 4.10 Dana car, into pulling the hemi-18 spline 4 speed and clutch disk and putting in a $100 4 speed OD we found at a swap meet. We got a new dual friction disk from Summit for the extra horsepower. Bought a new throw out bearing at the auto parts store.
You take the front retainer to a machine shop and have it turned down to 4.80-4.81" for $20, then reinstall it.
We were driving on the Hot Rod Power Tour the next year. We were cruising around 80 all week long and he loves it. The Hemi box is nice and safe in his garage for later. Everything looks stock too except for the one shift lever flipped over on the trans. He has less than $300 in the conversion.
I have the same trans on my Challenger. Bought it for $75 at a swap meet too.