I believe Lead Sled would only be used for full sized automobiles (e.g. C-Body Chryslers like the Newport, 300 and New Yorker, Caddilac Fleetwood, Lincoln Continental).
A VW Beetle, MG, Sunbeam Tiger, Corvette, Corvair, Mustng, Comet or Valiant would never be called a LEad Sled.
For me, the term “Lead Sled” usually conjures up images of an early-’50s Mercury.
Actualy I think that would be a boat. A sled would be an uncool car that lacks performance. A leadsled is a custom car with significant body mods (seams used to be filled with lead rather than bondo)