I suspect that you have a getrag 262 if it is a 4-speed. So you are looking for a getrag 265, which is a 5speed.
The one classic man has is a dog-leg close ratio box, most likely a 262-5, and they have a 1:1 top gear ratio, just like a 4-speed, the gears are just closer together, so it will not give you an overdrive to lower RPM at higher speeds. He could also have a 265/5 close ratio, also with no overdrive, and notoriously weak compared to normal 265 overdrive boxes.
I would recommend looking for a getrag 265(not a dog-leg close ratio), it will be cheaper as well, but there is a catch, the 262, 262-5 and 265 all use different drive-shafts, so if you are coming from a 4-speed you will have to have your shaft shortened, of get a driveshaft with the box.
Also, later boxes do not have a mechanical speedo output, I don't know if you need one, if not, you are in the clear.
Regards
Jacques