Originally Posted by SuperStreetJeep
what about using the 4.2 crank?
I'd have to look the numbers up and run them. But, I think you'll still run into a small difficulty with the compression height - I just can't say for sure off the top of my head.
Recall that putting the 258ci crank into the 242ci block also involves replacing the 242ci connecting rods (6.125") with the 258ci rods (5.875" - 1/4" shorter.)
And, whatever the difference is, I'm fairly sure it's not a full quarter-inch. However, I've been wrong before...
Quench and compression can be tuned slightly by head gasket selection - but that's usually only worth +/-.015" from stock, without machine work.