Hi SPCh. I am home from Uni, so here are my Serial Numbers:
Model 7 (Says 'MODEL 7X' on the front): 64424.A.556. This is on the scale-plate, and the 1, 1.5, and 2 on the Power scale have been added in red by hand, in the same style as the serial number. I guess this could have been a military one, as there is another number on the case (on the front, at the top) which is: ZD 02995, followed by the little arrow. The unit appears to have been serviced at some point by LIRC. On the working instructions on the back it says 'AVO Ltd, a member of the Thorn Group'. Plenty of info there!
Model 8: I can't see a Serial Number on this.
Where are they! All that is on the scale-plate is '8 IV'
If you want them, I can try and find the Serial Numbers for tha AVO Bridge and Signal-Generator I have too.
Sam