Ford 2150 2 bbl
The venturi size should be in a circle on the side of the carb, possibly hidden by linkages or brackets. There's a photo of where to look
here. Info on available sizes is
here (scroll down; not all the clickable FAQs are actually clickable).
If the number is obscured, blasted off by past abusive cleaning in a "remanufacturing" operation, or otherwise illegible, do you have a Ford number stamped or tagged on the carb you intend to use?