Gear ratios - 4 speed - 4+E

Ive been thinking about a 5 speed conversion for a while but after reading a few peoples opinions on their own 5spd conversions, im unsure what to do as they have prefered driving their mk1s as a 4 speed.
Im still running a 4 speed on my 1983 1.1. After reading that the ratios are not ideal in 3rd and 4th in the 5 speed box, ive decided it dont want to do that conversion, and ive been thinking about the 4 speed + E (overdrive box).
Does the 4+E have the same gear ratios as a standard 4 speed, + an extra gear added on for the motorway?
Or does it have the same ratios as the 5 speed.
I want to keep the cable clutch as i want the conversion to be as simple as possible.
What box would i need thats a dirrect fit onto the engine - i am aware the top gbox mount would need to be changed.
Also what selector would i need etc?
Cheers!