Ripper murders took place around 1888. Rembrandt Brown's police helmet shows ER (Elizabeth Regina - Elizabeth reigns). In 1888, Queen Victoria was on the throne and the helmet should have shown VR (Victoria Regina).
Wade opens the vortex in an alleyway well above everyone's heads, so there is no way they could enter it without assistance. However, the Sliders enter it by running up an unseen ramp. The shots of the alleyway reveal no inclines.
At 14:00, when Quinn calls Arthuro professor, the later gets irritated and claims that Quinn appears to be "shell shocked". The term "shell shocked" was coined during WWI. The events of jack the ripper take place around 1888, about 26 years before WWI.
Two actor tape marks are seen in the lounge right before Jennifer gets a round of applause.