RD: I found this spec for the '70 LT1 camshaft.. including lash specs. Your 0.026 on the exhaust may not allow sufficient expansion for a hot engine??

OEM part #3972178 is the original LT-1 setup. 242/254 @ .050 with 316/336 advertised, with a 116L/S. Lift @ valve .459" x .485". Lash settings of .024"-intake and .030"-exhaust.