I agree that if the engine is assembled, you are not likely going to get a 7/16" push rod to fit to standard designed BBC head. I can't remember, but I think either the exh or intake push rods only needed a single taper with the Dart 308 IE.

my springs are 236 on the seat and 671 over the nose

Performance Trend makes a 3/8 .125 one pc with tapered ends that will fit without any clearance work, we ran them with the Crower 68806 springs up to 7000 rpm.