300tdi rebuild?

I'm currently rebuilding my '96 300tdi 90 on a galvanised chassis and was planning on doing some work on the engine whilst its out. The problem i've been having with the engine is a huge amount of white smoke every morning when I start it and it also smokes a lot when im driving downhill and gently accelerating. I've changed the timing belt recently and noticed that the outer crankshaft pulley was wobbling around alot. after removing the pulley I could see that somehow because the pulley was moving so much the woodruff key had majorly worn away at the crank so that the key no longer sat snug in the groove. I also noticed that the crank timing belt pulley had a tiny amount of play allowing it to rotate a mm or so on the crankshaft, so shortly after I replaced the timing belt and bodged the woodruff key with some of that liquid metal stuff, it was back to its smokey ways. So i thinks I need a new crankshaft, but is this a job I can do myself? and if so should i re-new the pistons n rings and get it re-bored and honed etc... or keep it simple? The other
option i'm considering is just buying a 2nd hand low mileage 300 engine and just chuck it straight on the new chassis and save me the hassle, but if it's not too complicated to do the re-build I would prefer to do that as the engine would be better and last longer than most 2nd hand ones, I would hope. anyone who has any idea on whats best to do id be glad to hear it

before you change/buy the crankshaft you might as well rip the head off the engine and see what condition the bores are in. if theres a lot of wear in them you have to decide how much your gonna spend on the lump. you can get a 300TDi that has been reconditioned for just over a grand on ebay but youll need your ancilliaries. this would be a quicker route than throwing loads of money at an engine and you know it will be under warrenty.