408 personally, you also must also be careful when using a crank larger than 4.00 inch in a windsor block, it obviously can be done though. I had a guy put one together, didnt check rod clearance in the cam tunnel, well you know what happened when he started it

 

I have a 408, but I would go with a 427 if I had to do it again. But a 427 is going to need some serious breathing room, a 408 may suit your heads better.

 

anyone else?

 

I'd go 408 with your heads and intake selection . The clearances will be easier to obtain as well with a stock block .

 

thanks