Without resorting to Wikipedia, I'm guessing Pescara was about 16miles long. I think it was run around a lake (or I'm thinking of Enna), so might have been quite quick. If the average speed was around 120mph, then a lap would take 8 minutes...
This tells me nothing about where on the grid a 10 minute lap would be though, since I don't know the circuit length, nor the average lap speed.
I'm guessing 6th.