Whats the best time for a factory stock duster 1/4 miles ??

Bone stock 72 auto ,in drive with 355 and 275 radials 13.98. The Time slips before we bought it were in the mid 13's. My son could not get it hooked up. It took him 4 passes to finally get that time. worked his way up through the 14's. last pass he let it shift on its own. I guess he is use to turning right and sliding left. a good running 70 would go low 13's but not with him driving it.