Liberalism: a political philosophy based on belief in progress, the essential goodness of the human race, and the autonomy of the individual and standing for the protection of political and civil liberties.

Conservatism: a political philosophy based on tradition and social stability, stressing established institutions, and preferring gradual development to abrupt change.

Based on those definitions, who could argue that they were not liberals? By the standards of that time a conservative would have probably been a tory. Based on their social and fiscal philosophy, by todays standards they would have been extreme right wing

I don't think people defined themselves as conservative or liberal in those days but another way to ponder it would be to consider how they perceived the document. By adding amendments and three ways to add future amendments they obviously believed in modification of the constitution as needed. That might be considered liberal. However, by providing a procedure for amendment they seemed to believe in strict interpretation, which is conservative.

A favorite modern liberal argument is that the constitution is a living document and should be liberally interpreted to take changing values into consideration. Whether that is a good idea or not, I seriously doubt that the framers had that in mind.

You say that you don't feel comfortable wearing either label (with all of their implications). I agree that it is difficult to categorize people as liberal or conservative today. It is nearly impossible to apply the labels to to anyone that lived in that era.