Honestly at 200k miles I'm not sure I would just put head gaskets on it and expect it to last any amount of time. A complete engine can be had from the junkyard for fairly cheap. I know that Tilghman's likes to make an inventory of engines, and I know Blacey's had a couple of 3.4s sitting around the yard last time I was there. I also say that because running water in oil can be hard on friction points, and at that many miles it may not work out for too long.
If you decided to go that route, there are third gen guys that like to run the 3.4 in place of their 2.8, and could possibly use the crank, heads, or block
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