I will address these in order
#1. Yes, it is good practice to keep the parts in order, especially the lifters, as they wear to the cam.
As for the pushrods, they can be reused, check for galling and roll them as you stated, the pushrods and the stamped rockers are not as critical in placement as the lifters, but be aware of wear, with adjustable rockers- much more critical
Ok got it, at this point the lifters are mixed up, im gonna do my best to make sure they are straight and prob. re-use them. The rocker arms...Im assuming theres a right and left and only go on the one way.
#2. As for milling the pistons, yes, it can be done, but be aware that you would be taking quite a bit of metal from the piston face, it has been quite some time since I had those Trw/ Sealed Power pistons in my hand, but I don't know how much metal there is to play with, let alone the expense, as this would have to be done prior to balancing. Go with the thicker gaskets or get open chamber heads. I am sure you could easily sell those Eddies to offset a good amount of the price of the proper ones
I dont know what its like where your at but here is crazy trying to sell something, all of my stuff is worthless and all of theirs is gold. Im not giving anything away and Id like to use what I have but I do understand.
#3. The forged crank 340 is internally balanced, meaning the parts are weighed and metal is taken away or added to compensate for proper balance. The cast crank 340 and other externally balanced engines have special balancers , flywheels, converters to counteract the vibrations and balance issues. As for using the externally balanced balancer on the forged crank and trying to balance internally to compensate, don't even ponder it. The can of worms you would open for a 175 dollar part is not worth it. The amount of weight that would have to be removed or even added( really expensive) to make up for hanging that counterweight on the nose of the crank would be ridiculous.
IMO, for the type of use you are looking for, along with reliability, if you really want the 340, get the proper balancer, heads( to avoid the alignment issues from the thicker head gaskets), have the machine shop check and freshen the short block. Or sell the 340 to someone who really needs the date code and buy yourself a crate stroker motor and have a warranty and real torque without the headaches