Sounds like you were served up duff gen, mate! If the bores are .730, and the chokes are IC in both barrels, I strongly suspect it would be perfect for rifled slugs of any design, including the Winchester Fosters. Its just that the Brennekes are far superior for penetration.

If you check-out the info panel from the SABA web-page you listed in your previous post, you will see that the sluggie has "Improved cylinder chokes for slug."

I am strongly of the opinion that Fosbery-Paradox or Dixie Terminator slugs will probably tumble without spin-stabilisation. They are designed for rifled barrels or rifled-chokes. The shuttle-cock design of the Brenneke-type slugs is inherently better in a smooth-bore. Fosters are good too because they are nose-heavy with a lighter skirt, but they tend to flatten too much on thick-skinned game like buffalo.