how to make my nova faster

Hello,
I have a 72 Nova with a Blueprint Engine BP38313CT1.
it is quick but it isn't fast or not fast enough so that any corolla can pass me on the freeway.
The transmission is a TH350 and at most I can get a max speed around 110/115mph with too high rpm.
How to keep the current transmission and add one speed to it ? I guess this is not feasible.
So the only other option is to go for a 700R4 ? This one has 4 speeds, would this transmission allow to have higher top speeds ? Or is a manual transmission such as TKO600 recommended ?
I would like to keep it automatic. Also right now when using the lever I can shift down to L2 but not to L1. When driving in D mode it shifts automatically on all 3 speeds properly. It never downshifts by itself but I guess this is normal on older transmissions. Sorry I Am trying to learn as this is my first Nova and classic car, any hints and suggestions are welcomed.
Bear with me...

Thanks