I was at a swap meet this weekend and ran across an Edelbrock F548 Intake Manifold for Y-blocks. In looking at it I realized it had a different throttle linkage mounting holes and also a different vacuum port arrangement but the price was right so I picked it up. I figured with just a little fab work I could use it on my '57 Thunderbird. However, after I go it home and started to compare it to my stock manifold I realized the intake ports are much smaller (~.25" in both dimensions) than my stock manifold. I have done a search using the manifold number but haven't found much information on it. 
Does anyone know what the application is for this specific manifold? I'm guessing there were some small port heads made at some point and this is for them, but its a guess at this point.

TIA for any help