There's a guy here in Houston that buys and sells any type of crank. He has dozens of bb cranks and is at most of the swap meets. They are very nice. Personally, I couldn't think of a worse thing to have to haul around and unload all the time. I have his card at home. I'll look for it and post it when I find it.
In 1991 I purchased a brand new L-88 crankshaft to put in my L36 427 rebuild. I wanted the extra cross drillings that the 3967811 crank offered. At the time I paid $562 for the crankshaft. I still have the receipt. You may try your local Chevy dealer as it may still be available. Check the latest edition of the Chevrolet Power Book.
Check out Eagle and other brands. They have a variety of stroke and balance combo to choose from. All their cranks are 434 steel and are cross drilled and polished for a mere 700 plus bucks.
I for my 502 build up I chose the 4.25" stroke, internal balanced crank. Had the rotating assy. balanced. The shop said this was the best crankk he's seen in all his years. It had almost perfect balance. Very little drilling to get it perfect.