All of the original Ventures had positive flotation in the form of styrofoam blocks. Over the years, however, many owners removed some or all of these blocks to increase storage space.
The Venture 21 is a low, sleek, very fast boat with minimal accomodations. The 22 has a larger cabin with a dinette arrangement. Check this site for specs on the various models:
MacGregor Sailing home
Also check this site:
Look in the Owner Modifications area for original sales brochures, price lists, and owner manuals for the various Macgregor models.