Re: gear box, from petrol to diesel
the JTD 2.4 box is not dis-similar to the V6 petrol.
All this talk or torque, the 1.9JTD 140bhp is basically a V6 box with different cogs.
there really not that dissimilar.
whilst you could fit a V6 6-speed bos by changing the bell housing, you will find all the ratios are wrong and far too high revving.
Look on ebay, completed listings, as someone had a jtd box for sale for £150.
Buy what is wrong with yours, bad synchros? - can be fixed.
slight whine - probably just £50 quids worth of bearings?
Its probably not much and I would suggest a second opinion.