This would seem to be the item - I can't find anything else in that issue that he might have objected to:
Barnard's ultimatum
John Barnard has a deadline of Jan 10 to deliver his new version of the 1989 normally-aspirated Ferrari to Maranello, according to a leading Italian newspaper.
Our Italian correspondent, Pino Allievi, well-informed on affairs at Maranello, reports that the new Fiat-appointed head of Ferrari, Pier Giorgio Cappelli visited the Guildford Technical Office last week to talk to Barnard and see how the new car, described as the 'F1-89 Evoluzione', is progressing. The car is said to be profoundly modified from the first version which has been tested with little success at Fiorano.
The Jan 10 deadline is, apparently, extendable to Jan 15, but Cappelli has reportedly laid down another condition to Barnard continuing with Ferrari - he must work almost full time at Maranello once the car is completed.
Ferrari has reportedly approached Patrick Head's senior assistant at Williams, Argentine Enrico Scalabroni, with a specific offer to work on chassis development, but he has apparently declined the invitation.
There doesn't appear to be any follow-up to this item in the next couple of weeks, either by Autosport or from Barnard on the letters page.