Yayy! I've actually managed to make this work!
Ok, I revisited this when I planned to tune up my carb, got out my analogue multimeter/dwell meter and found it dead. Replacements are hard to come by/expensive/old so I thought I'd look into reading data from the ALCL and seeing if I can tune the MCS through that.
After re-reading my threads and picking up where I'd got to (really handy way of recording what on earth you were doing!) I thought I'd try to buy the read-deal FT232RL, rather than a clearly-fake eBay special.
A bit eccentric in the days of the internet, but I called the FTDI technical line for some advice, and they were really helpful!
I was advised to buy one of these:
https://ftdi-uk.shop/collections/usb...we-1800-bt_0-0
The advantage of the RS232 cable is that it contains and FT232RQ chip, plus a level shifter. This means it can cope with Voltages up to 15V, quite handy when your ALCL is pumping out data at battery voltage.
I simply plugged it into FT_PROG and inverted the RxD (received data) input and then went out to the car.
10k ohm resistor between pins A & B, connect GND (black wire) to pin A and RxD (yellow wire) to Pin D, fire up WinALDL, select 4800 baud and the 'CLCC car 1984, 1985, 1986' configuration. Key on.... and data simply started flowing.
After all that pissing about it was dead easy in the end - I just had to buy the right fricking cable in the first place!
My problem now is making the data usable.
Can anyone confirm what changes ALDL mode makes with the 1226865 ECM? I think it's advancing the timing, and possibly forcing it into closed loop. Does anybody know how to stop it doing this, so I can analyse the car when it's running normally?