replace 3.7 engine or head gaskets?

[charliep]

I have a 2004 Dakota with a 3.7 6 cyl engine and 198k miles on it. I began getting misfires then discovered that I'm losing coolant thru my exhaust. A mechanic shop quoted me $1,500 to replace one head gasket, $2,200 to replace both head gaskets or $5,300 to put a used engine in. This is too steep for my budget and I was pondering doing the work myself. I priced parts to replace the gaskets myself at approx $200 or I can get a 61k mile engine for $2,300. I have changed out engines and replaced head gaskets in older model vehicles but I'm not sure if there are any 'gotchas' with this engine. Can anyone give advice on whether I'm better off with the engine replacement or replacing the head gaskets? Any particular concerns I need to be aware of?