Unfortunately, there's not any way to get documentation from GM, but there's a lot of clues you can look for...
70 SS would have:
Round gauges
12-bolt rear axle
Boxed rear lower control arms
Rear sway bar (7/8")
Larger front sway bar (1-1/8")
Power disc brakes
3/8" fuel line (single line for L78 and LS6, 2 lines for L34 and LS5)
Bolt on flange where the ragjoint bolts to the steering shaft
Things that would indicate it's NOT an SS:
sweep speedometer
10-bolt rear
drum brakes in front
trim holes in the quarter panels just below the quarter windows (Malibu trim)
pressed on ragjoint flange
Also, the L34 (350hp 396) was available in the Malibu 400, so some of the bigblock stuff could be original, and still have been a Malibu.
Post up some pics of under the hood, body, interior, etc...
