They should be the same tube. Tung Sol was the only manufacturer of the 5998. We can thank Skylab for spreading this very useful piece of information originally.
There are a few variations on the Sylvania VT-231, but they should all have the same plate style. I've tried a number of different Sylvania tubes, but the original VT-231 isn't one of them since they have a reputation for light bass (not a good thing with my headphones) and because the various 3-hole plate Sylvanias from the early 50's are generally regarded as being superior overall. Not all of them I should mention, but some of them are..... or some the reputations say anyway. I like my Bad Boys quite a bit, but the real keepers have been some short base chrome tops from '52 which were made on the same tooling as the metal base tubes (I believe, it's so hard to be sure about any of this). The reputation on this tube doesn't seem to reflect my opinion, but I think I may have something different or more rare than people realized when I was talking about it. When I consider my collection as a whole, it is the black glass tung sols, then these, then everything else. I hold them in very high regard and since I managed to get two pair I'm running one full time now. It's a shame that pair has electrical/noise issues, but they aren't bad enough to stop me from using them.
There are quite a few variations out there for the Sylvania tubes if you spend some time looking, more so than most other brands. It's worth it to hunt down the great ones IMO.
