Thanks for the replies.
When the gearbox and diff ground to a halt my mechanic asked me to source a 2a or 3 'box instead of the supposedly weaker series 1 'box. ( we've owned it 29 years with the v6 in it, can't be that bad) . Once it arrived, it transpires that the id is marginally different and the holes are in a different place. I am informed by people who know a lot more about these things than I do that you can't just swap the bellhousing from a 1 to a 2a because bearing sizes are different.
My options are to find an adapter plate ( possibly like the one that AV8R has posted , thanks ) and fit the 2a 'box or even a series 3 box
Sell the 2a 'box which hasn't even made it off the pallet it arrived on! and have the series 1 rebuilt. But even that is proving difficult with parts scarce .
Any recommendations on where to go, who to use and what to do greatly received.
Charlie