By curious coincidence, you can actually use a GEM blade in these razors!
I kid you not! Pop the spine off the back, slide the catch aside on the razor and the blade will sit all the way back. With a little effort, the catch will slide back in place.
In the much later days, slim blades were issued ... kinda like Personna shaper blades but a little smaller.
Likewise, despite a really good and honed wedge, the shave was cumbersome at best to downright awkward. It's a phenomenal piece of kind and a curious piece of history. Good on you for trying it out.