[Clan]

Yes very hard to find a Transaxle now , it took me over a year of searching to find one ...

your 1983 4 speed will have the 3.82:1 ratio which is fairly low geared ( more revs when driving , feels lively )

The only 5 speed units with the 3.82:1 ratio are from the Diesel or the pre 1983 cars , we did not have the 5 speed in uk until 1984 did we ?

So you will have to find a transaxle from a 1.7 engined 340 with a final drive of 3.64:1
this will result in less rpm for any given speed in all gears and give a tall 5th gear .

I have this in my 1980 343 ( B14 1E ) and 1988 343 ( B14 4E )

I find in the earlier car it has noticeably reduced torque from the engine .

whilst with the later car in which the engine was revised slightly it works fine as volvo used the 3.64:1 final drive in later 340's .
It would be worth fitting the later B14 4E Engine if you can find one cheap , it has twin exhaust down pipes, computer mapped ignition ( RENIX ) and no radiator fan this does make a noticeable difference in power and economy .

I have a perfect low mileage M45R ( 4 speed ) 3.64:1 transaxle if anyone wants one !