Plenty of advice here, all free and all worth what you pay for it!
But in this case, I need a little more data as the car is on a change point. Up to 75, Toledos had a 3 rail gearbox, from 75 to the end of production in 76, a single rail box was fitted. These can be told apart by the position of reverse gear, the earlier 3 rail box has reverse to the left of 1st gear and the late single rail box has reverse to the right of 3rd gear.
The early box is shared with the Herald 13/60 and MkIII and early MkIV 1300 Spitfire and the single rail is in 1300 and 1500 Dolomite, 1500 MG Midget, Morris Marina 1300, 1500 Spitfire and last model 1300 MKIV Spitfires.
The gearboxes ARE interchangeable between types but it's a bit of a faff as it involves changing flywheels, clutches, propshafts and tunnel housings to suit.
If it's any help, I know where to lay my hands on a low mileage 3 rail box from a 73 Toledo.