I had a mk3 with an essex v6 and the gearbox fitted fine, infact when i removed it and fitted a Rover V8 and 5spd, there was very little to do to make the gearbox fit.
I must admit i cheated a bit as to get the Rover in i just bought a Rover V8 into Capri Conversion and adapted it for the Tina by using Range Rover mounts. The tricky bit was Converting the Car to Hydrolic Clutch for the Rover box but all in all its a prety easy car to work on with a rather large bay and tunnel