Where are you located.... If your anywhere near me.. Ill clear a spot on my bench for ya... and walk ya through it...
(thats not a offer that happens very often)
But to answer your questions..
The rod play side to side isnt much to be worried about (unless its EXCESSIVE)... UP AND DOWN is what you need to worry about...
as far as flushing the cases.... its a judgement call...
is it due for crank seals? are crank seals the reason the piston and rings went? or other things?
so on..
if everything in the bottom end is on the up and up, and only a SMALL ammount of alum went through them.... you can get away with flushing the lower end with gasoline several times, (or other various solvents)... But once again.. this is a judgement call...