Hi Pullark, If this was coupled to a generator it will have a fixed speed. This speed will depend on the alternating voltage required, 50 or 60 hertz. Probably 3000 rpm or 3600 rpm, this can be adjusted by a bolt with a locking nut. I believe this can be replaced with a variable speed throttle linkage, but I have never tried it and have no idea if Lister Petter would still stock the parts required.
You don`t specify what it is you are trying to propel but I have a restored old dumper truck from the same era, mine has a Lister SR1 engine but they were also sold with Petter engines. I suspect that the bell housing, clutch and gearbox might well fit an AC1, you might find one in a scrap yard. I think the gearbox and axle were made by Salisbury, in the UK
Bob