This doesn't answer your question directly, but I just finished a prog season where I started 1986 Dave Kingman at 3B for 81 games. He's rated D/D- at 1B, although his primary position is DH. He made 37 errors for a fielding % of .849.
Based on what I see in the draft center, D fielding 3B have RL fielding %'s of .880 to .920. So my guess, based on the assumption that Kingman's stats were nothing abnormal, is that Foxx would not be significantly worse than Cuccinello.