Looks like most of the Savage 24s were 22LR or 22Mag over a 410 or 20ga. There were some later ones made with 12 ga barrels. And some of the later ones were made with 17HMR, 22 Hornet, 222 Remington, 223 Remington, , 30-30 Winchester, .357 Mag, or .357 Max. barrels on top. I didn't see any 24s made in 308 Winchester.
Savage did import a couple of combination models with 308 Winchester barrels (a model 389 made in Italy and a model 2400 made by Valmet in Finland, I think). They both had the shotgun barrel on top and looked much like a typical over-under shotgun.