what crankshaft could i use?

I've enver heard that, but I'll admit, I'm pretty ignorant of 273 stuff. But, you could simply order up a 318 crank kit for a '68 318. Then you'll get bearings you need for rod and main, a good crank that works, and all you need to do is internally balance it with your new rods/pistons. I priced a kit for a 360 last week and it was $200.