This is the MOST frustrating thing I have ever had to do in over 35 years of motor maintenance.......

Sent the Lotus one back.

Weld broke on my fix - not enough penetration. Pushed out the spacer washer, cover and circlip somewhere between here and MK making that unit un-repairable.

Collected Speedograph unit from Post Office. EXACTLY THE SAME DIMENSIONS/THREAD AS THE LOTUS ONE I JUST RETURNED.

However, as there doesn't seem to be a single person in christendom that knows the right part number/other model equivalent I have decided to order a new angle drive adapter (the bit that clips onto the gearbox with the Y bracket) from Lotus, so that will then fit the new angle drive perfectly.

So, for future reference:

Part Number for Morgan 4/4 1600 - known only to God
Part Number for Lotus Elan equivalent: BG2402/03
Part Number for Lotus Elan adaptor:FZZZ026Z (Paul Matty)

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10