In article , dave wrote:
Has anybody got (or can tell me where to get) any datasheets / pinout
info on RF modulators made by Astec, particularly the UM1233 and
UM1287 models.

From 1985 Maplin catalogue:
____________
UM1233: a Supply +v a----| | Case=GND
b Video in b----| |
c none c----| |
d none d----|________ _|
|_|

Supply +5V @ 6mA
Bandwidth 8MHz

UM1286: (yes, I know you wanted the UM1287 but maybe it's close?)
a Fine tune
b Audio in
c Supply +V
d video in

Supply +5V @ 9mA
Bandwidth 8MHz
Sound carrier 6MHz

Regards,
Mike.