Hello, that 71 skylark should hold the first tire with no problem..it is basically the old L 60 15, I know I am old...but if you are running a big gear, such as a 456...it is a little short...The biggest tire i could get under my Belair was 29.5 inches tall without bending metal in the front..If you have a local place you usually go, they might dry mount the tires to see if they fit...and if they don't try another..The place I go in Hilliard let me do that..I searched for months trying to find a tall tire that wasn't to wide...etc..It basically came down to there are not a lot of choices in tall and narrower street tires..Also, the rim you are using, offset etc. makes a big difference..Try this link it may help...
http://www.wheelsmaster.com/rt_specs.jsp