I'd say they all rust out equally, my 75 ventura Custom was the rustiest car I ever owned, and thats saying a lot for NY rustbelt.
More likely the non-Nova ( olds / buick as noted, even moreso than Ponchos ), were better-kept, "high-end" cars bought by people who garaged them and basically babied them more.
As for my own recently purchased 'traitor' car, lol - how about a 78 Pontiac Phoenix hatchabck, 305 auto, with 29K original miles
http://cgi.ebay.com/ebaymotors/ws/e...d=1,1&item=4646059605&sspagename=STRK:MEWN:IT
unfortunately the hatch leaked for 25 years and the trunk / spare tire well is rotted out.
anyone got a hatch lid for sale ?
rest of the floor is nice, with minimal surface rust in a couple spots ( POR 15 and it will last forever).
typical interior ( non-garaged ) heat baked plastic trim, which will need a lil work, otherwise nice and clean - and only 3224 built in 78 ( hatchbacks, not sure how many were V8s ).
~ AL
and, to tie in to the question, most Nova parts should fit a Skylark, except lights ,grille, trim,etc - quarters might need trimming aroung the tailights if you need those - specifically what dies your Skylark need ?