According to the Encyclopedia of Modern Firearms from Brownell's, the sport-king came in 3 main variations. The light weight, light weight deluxe and the all steel model. The illustration in the book show the l.w. & l.w. deluxe as having what appears to be the two lugs beneath the barrel. The all steel version has a single lug beneath the barrel.
Model #'s for the l.w.: 9156 4.5" bbl, 9157 6.75" bbl, 9158 combo.
Model #'s for the deluxe: 9103 4.5" bbl, 9104 6.75" bbl, 9105 combo.
All steel #'s 9200 4.5" bbl, 9201 6.75" bbl, 9202 combo.
the book also shows that the firing pin is the same for the following models: sport king, field king, supermatic and olympia model pistols.
Hope that helps
[This message has been edited by marcel ledbetter (edited 1/23/2007 1:05p).]