Stock number 1974 what size engine is this 7.3?

Well 7.3 Liter is 445 cubic inches if that's what you're asking but for those details you have to contact the seller directly. You are in the wrong place, there are 300+ listings

where did you see 7.3, ford offered a 460 cubic inch eng. in 74

Dealer stock number 1974...2009 model year but for that matter all they offered was the 5.4 in 2009 F250---- and 4.6 or 5.4 in F150, Reg Cab, Super Cab, 4WD, 2 door 4 door whatever ----for gas anyway, then the Powerstroke diesel there was indeed 7.3 from 1994 until 2003--- also SB in the model means Short Bed