Destroked 318

old school would just run another bearing as a spacer. You could also get some shim stock and bend it up and notch it if possible or just pin the rod. These look like you'll need to turn down the crank .025 for the smaller big ends of the Chevy.
Eagle SIR rod comparison, very close specs 6.123 and 6.250 compared:


6.123 rods
Approximate Connecting Rod Weight (g):605

Rod Journal Diameter (in):2.125 in.

Big End Bore Diameter (in):2.2500 in.

Pin End Bore Diameter:0.984 in.

Big End Width (in):0.925 in.

Pin End Width (in):1.060 in.

6.250 rods
Approximate Connecting Rod Weight (g):615

Rod Journal Diameter (in):2.100 in.

Big End Bore Diameter (in):2.2250 in.

Pin End Bore Diameter:0.927 in.

Big End Width (in):0.940 in.

Pin End Width (in):1.060 in.