If you’re having trouble envisioning Ibrahim and Sereno’s Spinosaurus as a biped, even with the updated limb proportions, I direct you to the above video about pangolins.
Pangolins are (as far as I’m aware) the only mammals with a theropod bauplan, that is, walking on two legs with a horizontal body posture. Mammal hips aren’t designed for this sort of posture though, but pangolins has to walk like that because of their specialised forelimbs, so they’ve got a bit of an awkward, hobbling walk.
The long, low body, short legs and even the arched back of pangolins reminds me a fair bit of Spinosaurus, the proportions don’t seem that far off IMO. I could quite easily envision Spinosaurus walking bipedally like this, with its hands only just off the ground and with short, quick steps.
Rather suits it, I think.