I wouldn't trust them either. The '68 sits most of the time, and about 10 years ago, an 8 year old tire with maybe 5,000 miles on it blew up UGLY. No rot, wear and rarely seen the sun. Luckily, the out of style running board took the beating instead of the fender.
A friend has an '88 Formula he bought new. About 35K on the clock I think. Still on the original rubber. He wanted to take it on a trip a few years back, I told him he was crazy. So rather than buy tires, he parked it
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'68 GMC shortbox 4x4 350/SM465/T221- bought it in '83
SOLD 
'72 K20 500 Cad/TH400/NP205
SOLD
'92 Chevy 2500 6.5 mech TD 4L80E crusty daily driver
'72 Monte Carlo... sweet low mile toy
'11 Dodge Challenger IE 392 6spd... midlife car
