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Different pushrod lengths on each side wont be any problem, if that is what ends up being required. Frankly, the different lengths have always been somewhat confusing to me, one of those things that just doesnt stick in the memory bank.
He has pushrods listed in two places. In one 3 separate pushrods are listed '54-'55, '56-'59, and '60-'64. In the other 2 are listed, '54-'55 and '60-'64, and '56-'59. So I'd guess you need the same pushrods.
The difference is about 1/64" which isn't much but the longest pushrod you can fit will provide the greatest rocker ratio. You could take it a step farther and shim them for the best geometry and order custom pushrods.
I have enough stock 1964 length rods on hand and then some. If you set your lash correctly it should cause no issue other than the ratio and angle being off slightly.