Doing the engine swap.

So as I am sure most of you guys already know, Toyota messed up on the engines from 1998-2003 and put too small of piston rings on leading to massive oil consumption and engine sludge finally ending in complete engine failure. my 2000 GT hasnt been running so hot lately and im thinking my engine is close to dying. So, because of this, im left with two options, rebuilding the engine (piston rings, gaskets, cleaning the valves, head bolts, the whole sha-bang), or just dropping in a low mileage engine from a 2003+ engine in it. has anyone ever done either options themselves? and how much of a pain is it to do either of them. I can get an engine with less than 50,000 miles on it for like 6-800. so just let me know how much FUN it is to repair this issue.