Looking at your other thread, this is a mild 340 build. Your stock 5/16 line is more than enough for that. How high are you trying to rev the engine and at what rpm is it starting to fall over.
I'm seriously doubting this is a fuel delivery problem.
I never take it over 6500, it starts to fall at around 5000, 1st and 2nd gear there is no problem. once into 3rd at around 5k it starts to miss and stumble. Could it be the coil? it's happened to me once before.
I've tried jetting up and down from where it started with no change.
and to the question asked about what jets? 71 pri 79 sec.