Hi MF,
The Lycoming flat four used in the Cessna is a bigger displacement than the V8 in my Fairlane!!
The Bell 47 helicopters like the one used in Skippy uses a six cylinder version mounted standing up.
No; 'read my lips' - they're Continental flat sixes.
Tho' Textron Lycoming do make a 320ci flat 4-cyl; my old Uni mentor had a 'zero time level' complete overhaul done locally [Rudy's Aero Engines, West Sale] on one of those, for his Cessna 177, a couple of years back.
Out-of-pocket cost $16k; and that was with a $1k credit for 'donkey cleaning work' Ray performed, post bead blasting of the crankcases...