You're not giving enough information to answer your question. Also, positraction is a form of limited slip. Read up on the matter here or elsewhere on the internet.
Top end speed is a function of
rear axle ratio
transmission ratio (I don't think a 700r4 can stay in overdrive past half throttle so you may be at 1:1 in 3rd)
car drag coefficient
engine power output
max rpm of the engine
Those are just the bits off the top of my head, there may be other things you need to determine as well.
I am running 3.73 with a 700r4 in my 1969 Chevy C-10 and it will hit 130. I did have to change a part in the tranny to allow it to stay in OD past half throttle as DMC said. Summit sells the part for about $40, also bowtie overdrives has it. The thing is, I am running 31 inch tall tires, so a street car tire would be different. It runs about 3500rpm at 125.
It was running 4500rpm at 120mph with what gears? If I remember right stock gears on those cars were pretty tall . . . somewhere around like 3.07's. You might be able to obtain that speed with the 700 and the overdrive mod but I still dont know if you'll be able to do it. I still think overdrive will want to kick in. Like dmc said it will depend on many factors, one of which being your engines output. How hard it will have to work to advance to, and then maintain that speed. Is this just a cruiser or is it going to see the strip? Strip Id say go with the 3.73 . . . a cruiser Id reccomend 3.42's.
I wouldn't suggest building a car around the idea of obtaining 120mph simply because you might only see that speed 1 or 2% of its driving life. Cars that can reach that in the quarter aren't meant to cruise at that speed. They are pushing it to the limit.
I installed the GM valve that was designed for the 1989 Police cars to keep it in fourth gear during pursuits and to stop engine overreving and overheating. I do not think it is any good on the drag strip . the trans (in D4) will upshift too soon then downshift from fourth to third during high speed coast down . IT is good for long fast driving to keep engine RPM,s down and temperature normal.
is it bad for your trans to be driving around in od? some guy today told me that he was told that if you drive your car in the od gear then it will burn up your overdrive is this true? he also told me to drive around in D because it was better for the trans is this true?