JAGUAR E-Type 2+2 Series 2 - Auto E-Types

Q
I have a 1969 E-type 2+2 Series 2, with a Borg Warner Model 8 automatic transmission, and I am thinking of having it totally gone over by a reputable transmission shop.
Before doing that can you suggest an alternate automatic transmission that will fit the car to improve the performance, reliability and economy?

A
If you are prepared to consider a manual transmission, the overdrive gearbox from a Series 1 or 2 XJ6 is a very easy conversion to complete with the larger transmission tunnel in the auto 2+2 allowing plenty of room.
Otherwise it may be worth considering a Borg Warner W Model 12 transmission, as it is stronger, has a more reliable electric kick down, and is internally the same as a Ford FMX, for which there are plenty of goodies available to trick it up, especially on your side of the pond.
If you are looking for an overdrive fourth gear, the best option is the ZF4HP22 from either a 3.2-litre or 3.6-litre XJ40, or a 3.2-litre X300. Conversion kits are both available in the UK and US.