Funkierthanfunky

I have version 2 type ra which is running a 2.5 but has killed it's gearbox. The gearbox was fitted with WRX ratios and retained the DCCD so it didn't have the short RA ratios.
I need to replace the box with a 6 speed (with DCCD) to take the torque of the 2.5.
However.....
A JDM 6 speed would be the easy choice except, as I could keep my rear diff, it is very low geared, almost identical gearing in 1-5 as 1-5 in the Ver2 RA with 6th just slightly lower than I have now. Although Dave at API reckons a JDM box will be too low geared and work the new 2.5 motor too hard.
A UK box would have to be a late model one with the longer gearing which are rare and expensive and.... would need the rear diff changing for a 3.54 ratio.
I would like to keep the lsd in the rear from the RA though so I have a couple of questions.

Has anyone got experience of running a 2.5 on JDM 6 speed in a classic? If it helps I use the car almost exclusively on track days or at the Nurburgring.

Has anyone put the internals (i.e. lsd mechanism) of an RA into a UK rear R160 rear crwonwheel to make a 3.54 with an RA lsd? ( I have done this before on a BMW E36 using a 5series LSD removing it from the 5 series casing and fitting my crown wheel from the E36 and then refitting into the E36 casing to make an LSD with the correct ratio in the correct case ).