Sorting through some blocks for another build. I have a 318 whose #'s says its from 1976-79. Before I pull it apart, I think I remember that the 76-79 motors came with HD rods with floating pins and the cranks were good for 6500 rpms. Just building a motor to run 12.0 with a 3300 lbs A body.If I don't need to use one of my truck forged cranks then I can save it for another build.Am I remembering correctly?

No, you're not.

The post 1976 318s DID use the 360 style 645 rods and a regular 318 cast crank.
They were pressed pin, same as all 360s and all the 645 rods used on 318s, which may have started as early as 1973.

I have never heard of a cast 318 crank having problems with strength.

The 645 rods weigh 758 grams apiece. You can save around 150 grams EACH by changing to a light aftermarket rod. Add a piston like the KB 167 and save a total of 240 or more grams PER PISTON. That's more than 1/2 lb per piston.

Even the early "skinny" 318 rods are 726 grams.

A piston and rod from a 318 weigh like a bigblock set from other than Chrysler engines.

R.