We need much more information regarding this engine rebuild!!
Which rocker arm system is installed? What was done regarding the camshaft itself during the rebuild, is it "stock"? Is it a regrind? Was the base circle size on the camshaft lobes reduced?
There are two different camshafts used on these engines, one with the fuel pump drive towards the rear and one with the fuel pump drive at the front.
Was the cylinder head completely rebuilt? By a machine shop?
There should be no reason to use any different pushrods other than if the camshaft itself has had it's "base circle" reduced.