I have some old Airfix magazines and here are some issues that have WW I vehicle conversions in them:
Nov 1968 WW I salvage tank
Apr 1969 MK II supply tank and MK V female
Apr 1968 may have a MK IV conversion in it
October 1969 Ford T ambulance 1/32
Jul 1969 pigeon loft conversion from a B type bus
Apr 1970 Rolls Royce armored car scratch 1/32
Apr 1971 military model T's 1/32
Sep 1971 Austin armored car scratch 1/32
Feb 1973 Ford t hucks started conversion
Jun 1978 Karrier Charabanc conversion
There is an Airfix modeling site online somewhere you might be able to get more info on these conversions there. I did the WW I salvage and Supply tank conversions decades ago. This is when the Airfix WW I tank was the only WW I tank kit around. I hope this of some interest.