2000 Grand Caravan 3.3 Cylinder Head Gasket replacement

As indications are the cylinder head gaskets are the problem, I'm going to dive into replacing them. Before I get started on the job, I want to have all my ducks in a row. Namely, all the parts/gaskets on hand.

When pricing the parts list, I see there are two styles of valve covers: 9/32 and 29/64 bolt holes. Also mentioned is isolated and non-isolated. How can I tell the difference without pulling the valve cover? The bolt is retained in the grommet. The bolthead size on my 3.3 is an 8mm socket. The bolt diamter is approx 1/4". Can I assume I have the 9/32?

Of course, I'll have the heads checked for cracks and warpage once I remove them. In web searching for cyl heads from salvage yeards, I've found a set for reasonable cost that may be worth the investment. If I use these other heads, should I purchase new pushrods, or re-use the rocker arms from my heads, or what? Are the heads for this 2000 3.3 all the same? Are the two valve covers (isolated and non-isolated) interchangeable? Also, as my 3.3 is FlexFuel, does this make a difference? I just want to avoid problems with part interchangeability.