From an earlier post (I am sorry) I forgot who it was
"At the very least I would stroke a fresh 318 to 390ci or so and put either 302 or 308 iron heads on it with a cam designed for your combo at that elevation. Or as others have said TURBO on a good healthy engine."
There are several shops out there that have either a steel or a cast crank package with high compression pistons and good rods for $1200 to $1500 Leave the rest of the combo alone. I am planning that same deal for a truck 360 that already is .030 over for my D100. I may have to go lower on the compression because I live @ 600' (at the foot of Mt. Rainier) and you can get away with more. Good LUck