bcp is correct that the 98 has a third safety lug which is missing from the earlier Mausers, however you have to get a look at the bolt for that. The most obvious visual difference to me is the bolt shroud/sleeve, which is at the rear end of the bolt. At the front of the bolt shroud on Model 98 (just behind the bolt handle) is a gas-deflecting flange which is larger diameter than the remainder of the shroud/sleeve. This is a patented feature of the 98 which is absent on older models. Looking at the silhouette of a 98 vs, say a 93 or 95 Mauser, if you follow the bolt sleeve forward from the rear it forms a straight line on the earlier models but has a little bump up on the 98 just before you reach the bolt handle.
The Husqvarna models that were modified from the 98 Swedish Mauser also have this flange (which was presumably copied from the later FN streamlined bolt sleeve that lacks the sleeve safety), but what the Husqvarna lacks is the internal gas collar in the receiver ring. That was also a patented feature of the 98 system, and among other things makes the 98 easier to rebarrel, according to gunsmiths, than any other bolt action rifle.
