See my site www.leeuwinga.nl
Lot,s of stuff about Harrison T280
Of course it is all in Dutch but you can use Google to translate
it into English.

Harrison can be succesfull be controlled by a PC.
Turnmaster Pro from Microkinetics is most suitable
However some of my customers used Mach3

The old computercard (BBC128K) need to be removed
as well the two index cards, screen and keybord panel.

On most of the lathes the drives are OK, so you can tap
direct to the existing drives.
The whole will upgarde your lathe to a full cnc lathe

The only disadvantage on Harrison T280 is the fact that there are
trapezium screws on Z and Z axle for a good CNC application
you should change this to ball bearing scrwes.