I see this is your first post, so, first thing's first, welcome to the site.
I considered going to a manual so I could get overdrive, but, as I have gotten older I prefer an auto ( it never misses a shift ) I know other's will have more info, but till then...
A few things to consider. Do you want it to be all stock? If it doesn't have to be all stock, you can you a hydraulic clutch set up that gives you more options, and clearance. Have you considered going to a 5 speed?
If you stay stock you will of course need to install a 4 speed tunnel, but they are readily available. So a little more info will be very helpful and we all like to see pictures