The only way you will really know is to get it on the track. The single exhaust will really hold you back. even with a 351W and street gears. You get headers better gears and a good 4V intake and carb combo you could be flirting with low 14's
My dead-stock 73 vert (351C-4v, C6 auto, 3.25 open gears, 15" tires) ran low 16 second quarter miles. I think 16.3 was the best it ever did. All other things being equal, I would expect your 351W to be about the same.