This is an old post that I came across, but I thought I would reply to it. I have two combination guns, one is an Italian made Sabatti 12ga over 6.5X57. Very nice gun with engraving, double trigger and the rifle barrel having a set trigger. The second and my favorite in a Valmet 412s, 12ga 3" over .223; not as fancy as the Sabatti. The OP is correct about the Savage 24 barrels being off. What's nice about the Valmet 412s' is you can adjust the rifle barrel to hit were the shotgun hits. I have a scope on mine and adjust the scope so the shotgun pattern is centered at 40 yards then I adjust the rifle barrel to hit were the scope is aimed at 100 yards. I believe the Valmet 412, Tikka 512, and Marocchi 512 guns are the only combo guns having this feature. Valmet sold their tooling to Tikka then Tikka sold the tooling to Marocchi. Marocchi is currently making the 512. These guns are pretty expensive today. In the late 80's and early 90's they sold for approximately $500.00. I purchased my Valmet four years ago, unfired in the original box and sealed with cosmoine for $1600.00. You don't see many of these and far fewer with a .223 barrel. Any Valmet barrel set will fit on the Valmet 412 receiver. They came in double rifle barrels and double shotgun barrels and various combination set ups.
Correction: the Marocchi is now called the Finn 612 and comes in these rifle calibers 222R-223R-30.06-308W-6,5×55-7x57R-8x57JRS-9,3x74R.