As far as the need for a shorter or longer pushrod.The only adavantage would be to correct the rocker geometery .The geometry could cause a breakage issue.An easy way to check if you need a different length is to remove the rocker arm .Remove the oil film from the top of the valve stem and the contact area of the rocker.Use a permanent black marker and paint the top of the stem .Reinstall the rocker and adjust the valve .Turn the engine
360 degrees and remove the rocker.Look at the top of the valve stem and see if the contact is in the middle of the stem.If the contact area is away from the rocker stud you need a shorter pushrod,if it is closer to the stud you need a longer pushrod.As far as milling the head .125 it is possible but that is crap load to mill.Normal milling will remove .004-.005 at a time from the deck surface .Have you measured a head for thickness that has not been milled ? It would not be advisable to double up a gasket it wont seal.You may be able to find a manufacture that makes a copper shim to use with your gasket .Have you checked the valve stem height? Good luck
