MatB

You will need a serial link and assuming your laptop doesn't have a genuine old school 9pin serial port you will also need a USB to serial adapter (computer store).
you will need pclink v2.5 available right down the bottom of the downloads page: http://www.linkecu.com/software-support/pc-link-downloads/

Yes that Sub-board will suit the H22a. You will need to wire trigger 1 to the 4 tooth pickup in the distributor trigger 2 to the single tooth.
 

To connect a pc to it you will need a "Serial Link": http://dealers.linkecu.com/SER  they are still available new and cost about $120 in NZ.
Note however these old G1's didnt have configurable trigger inputs - to allow them to work on different engines they needed a different "sub board" fitted.  It was quite common to change these over time, hence Simon's comment above "Assuming the ECU is unchanged from when it left Link".  So to confirm this you should open up the case and give us the numbers off the sub board or post a photo etc.  The sub board is the smaller PCB that sits above the main board, about 40mm square I guess.
So my suggestion is dont buy a serial link yet, confirm the sub-board is correct for your engine first.