more vauxhall victor help please!!!

If I were you I'd look at what the engine will cruise at.
Let's assume that the engine will cruise a 3000rpm quite happily and that you have your original axle. 4th gear is convenient as it's 1:1, so we can forget the rpm/torque multiplication that occurs within the gearbox.Let's see how this works out:

At 3000rpm in fourth gear (1:1) with a 4.1:1 rear axle and a 22.7" tyre diameter we would be doing 49.4mph. Maybe going bigger on the tyres and having your speedo recalibrated would be cheaper in the long run? Remember though, that good performance relies more on good gear ratios between eah gear than anything else. It's an area that's often overlooked.