I have to agree that from the standpoint of cost and the straightforewardness of the swap, the windsor is the way to go. Run away from any 351M. Obviously I went the Cleveland route, but I had the engine before the car. Also, just to point out, the C only weighs about 70 pounds more than a cast iron intaked carbed 302, so weight isn't really a legitimate reason to rule out the C. Now the $430 and up swap headers and $300 oil pan and pickup tube, that may be a good reason. Another plus for the windsor is that you can stay fuel injected if that's your bag.
How to ID:
Windsor: 6 valve cover bolts
fuel pump bolts side by side
thermostat in intake
cast aluminum timing chain cover
Cleveland: 8 valve cover bolts
fuel pump bolts vertical
thermostat in the engine block
flat stamped steel timing chain cover
intake about 8.XX inches wide
Modified (M): same as cleveland except:
intake 10.XX inches wide
front intake sealing surface of block about 1 inch above front block extension where dist. and tstat mount.
The intake widths are from a foggy memory, but the M is about 2 inches wider than the C regardless of the actuall measurement (which can be found in Edelbrocks intake listings)
I've been long winded enough.
