50-52 235 w/powerglide and all 53-62 235/261's have the larger ports.
37-53 216 and 41-52 235 w/manual tranny have the smaller ports.
Most of the vintage intakes you will find have the smaler ports. You can still use them on the later engines, it's just that the intake alignment rings won't work. You can have the intake milled out to the larger port size if you want to spend the time/money.
Offy still sells both versions.
Also, the way the intake bolts up to the exhaust is different between the two types, but if you are going to run headers, then its not an issue.
