rough Idea on compression ratio

Looks like you are there with those pistons and Mr Gasket 1121G head gaskets....Those are pretty close to the stock shim head gasket thickness. BTW, the catalog says that the pin is offset in those pistons, so they need to be installed in a certain direction.... notch to front would be what I would expect.

Are you boring the cylinders? Your original description posted is for stock 4.040" pistons size. If the bores are worn or tapered or out-of-round, your engine may not do well without overboring.

The listed Sealed Power ring pack for the 340 is the E286K. The ring heights are the same for the E251K's for the 360 but there may be something different like in the ring twist for the 340 vs 360. The E286K crosses over the a Hastings 2M694, which is a moly faced top ring set that is a little less expensive. I can't say anything about the relative quality of the 2 brands.