Classic LT77 Short stick to long stick conversion

Dear all, I've been following this forum for quite a time and it has been very interesting and useful.
Recently on my 1985 Range Rover classic V8 petrol manual, I swapped the gearbox (because of worn output shaft) as I do not have enough tools and experience to disassemble the Lt77 and replace the output shaft only. unfortunately the parts seller mistakenly gave me the short stick version and I only noticed that when I had already removed my existing gearbox and was planning to swap the shifter. After some research, I found thread here explaining how it's possible to make the conversion.
So I got the R380 adapter from Ashcroft and followed @jamesmartin s advice, swapped the endcap and assembled it. It shifts and drives as supposed, however there are 2 points I need your advice:
1. the rear T piece for gear interlock spool is missing from my existing (old) shifter. is it straight bolt on and will it match the position of the spool ?
2. 1st gear makes noise (sounds like reverse gear) only when loaded, under acceleration. all the other gears are quiet. I asked Dave Ashcroft about it and got an answer - The noise in first will be the 1 / 2 outer fouling the reverse gear. I trust his expertise, just don't think I fully understand what it means. could you please help me with this also ?

P.S. I contacted the parts dealer and he apologized and said he can give me the correct gearbox anytime. BUT I was limited in time as I am booking a garage to work on my car and decided to go with what I already had and try to make it work with an adapter, as he is located a bit far.

Sounds like a right faff, I'd put the box it should have in it and make things easier for yourself kiddo..

and all the time 1st gear is rubbing on reverse gear, you are making metal filings, for the oil to circulate around the box

Mark Piercy said:

Sounds like a right faff, I'd put the box it should have in it and make things easier for yourself kiddo..

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+1.

Unfortunately, James no longer shares his knowledge here.

Mark Piercy said:

Sounds like a right faff, I'd put the box it should have in it and make things easier for yourself kiddo..

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I think I will do that.
So, my suspicion is that, even if with the adapter, the gearbox is shifting (more or less) properly in all the gears, perhaps the position (i.e. the length of the adapter) may still not be precise enough. So the reverse selector fork is not returning back to its original position and ends up rubbing against the 1st gear. To avoid this, I should machine another adapter, play with dimensions, experiment and even if I manage to not have the noise in 1st gear, it still does not mean that the selector is in perfect position and working properly.
So yes, instead of faffing this much, I'd rather go back, grab the suitable gearbox and install it properly

Western Slope Rover said:

Unfortunately, James no longer shares his knowledge here.

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That is sad news