You might want to check in over at slantsix.org. I think,, and may be completely wrong but something like cam bearings need to be changed or some machining needed to feed oil to the lifters. I remember reading something,, but again I may be wrong.
No, but you do need to use the right pushrods with holes in them.
And I THINK you could use AMC lifters if you wanted to try a high-leakage type lifter. They are designed to oil from the side and pump up through the center, but I don't know if they would work to oil from the top.
I investigated this idea too but gave up on it because of too little benefit for the trouble.