Regarding converting an OD 5 speed to a 1:1 5-speed - it is theoretically possible with a 60L (ie the dog-leg 1st box. The reason for this is that the standard box's 4th/5th shift rod uses a 'flick-over' lever to achieve 1:1 4th where 3rd would usually be in a standard 4-speed. If you eliminate this in a standard box it would swap the position of 4th and OD 5th. Then you use a custom gear-set with what was OD 5th as an under-driven 4th gear followed by 1:1 5th.

Stock pattern & gears)
R-2-4(1:1)
1-3-5(O/D)

Stock gears/mod'd pattern)
R-2-5(O/D)
1-3-4(1:1)

Mod'd gears & pattern
R-2-4(U/D)
1-3-5(1:1)




..... However, I remain sceptical this box has had this done until I've seen a picture of its internals.