Buying an engine?

Looking at buying another 200 tdi engine to put in the 110, the last one I bought the whole car, but i've been offered one out, but its been stood, garaged for two years! is there any thing i need to look out for or do before instaling it or even buying it?
The last one blew the head gasket, warped the head and did bottom end damage, (not sure how bad or what) is it worth rebuilding the old one or buying a mystery one or try and buy a complete car running?

rusty bores where rings contact if damp storage for 2 years

will that just be surface rust or will it affect the rings? I was thinking of giving the engine to a good landy mechanic and let him rebuild/replace bottom end, rings with the 300tdi like you said before and put a 300 head on, at least i would know whats been done?

Rust can score the bores and result in poor compression and blow-by. General result from that will be poor performance and maybe even an engine runaway if the blow-by is enough to force oil into the intake.