making sum assumptions, i calc'd out the cfm for the 351...
My assumptions were:
max RPM is 5500
volumetric efficiancy is 85%

With that given, it calc'd out to 475 cfm. The 650 is a little big but it is a good carb. i would try it, if it bogs a tad then try jetting (fuel) it down by 12% and that should put you right in the ballpark of where you need. (if the jet size is 72, multiply 72 times .12+ 8.6 or jet #64)