Gday All

I have an 85 County that was v8 and have converted to isuzu 3.9 running an lt95. High range transfer case gear ratios have not been changed since engine change but I did have have higher ratios put in for the v8, cant remember the exact ratios but it used to rev at 3000rpm at 110kph with 32" tyres. Am fairly sure that gear set put in was not 0.996:1 as remember one gear being bigger than the other. This seems to be working ok for the isuzu but have just purchased a gearbox containing a set of 0.996:1 gears and was thinking about using them. Get reasonable fuel economy (10L/100km) but is VERY noisy on the highway (I know its a rough as guts truck engine but other isuzu counties i have been in have been much much quieter, mine has heaps of soundproofing and was very quiet at highway speeds with the v8.) and was thinking this could be due to the engine revving too high.

What gear ratios do other people run successfully and can anyone tell me what revs the 0.996:1 gearset or isuzu gearset will give me? And lastly can anyone give me some tips or the process on how to swap these gears have the spare box to practise on before I stuff up the the one in the car. This topic is not really covered in the landrover workshop manual i have, is it covered in the Haynes or other manual?

Thanks in advance

Luke