These models take a small strop that passes through the body of the razor just under the blade, right? Like the Valets? If so you will find that the limiting factor (for a new strop anyway) is the physical width of the leather. If you have useful old strops that fit, make sure they are good for purpose - not covered in gunk, pastes, wrinkles or nicks.
If they are a bit 'iffy' and stiff, or have nicks very fine sandpaper (wet and dry, not proper sandpaper that leaves bits of grit everywhere) of around 400 - 600 grit will let you sand the nicks out - you are only concerned with what stands proud of the surface of the leather here), followed by saddle soaping - this should put a bit more life back in the strop (make sure the strop is perfectly dry after saddle-soaping and press it flat in a tea-towel under the weight of a book). If despite all this the draw is still to fast and you want a bit more drag, lightly dampen (not soak - just rub with a damp rag), drop a single drop of neetsfoot oil on another bit of rag and rub it quickly all over the surface. You want barely enough to cover it - too much and you will ruin it. If it isn't enough you can always do it again, but it is super-hard to take it away if you put too much on.
Because the thickness of the leather was a factor, they tended to use thinner leathers, like shell and pigskin. Both of these have a very fine surface and both are very good, the shell perhaps being a bit finer and quicker on the draw than the pigskin - but it all depends on how they were were tanned, so you will have to use your own judgement! If one has a quicker draw (ie, a lighter feel while stropping, offering less resistance to the passage of the blade) then you will need to do more laps to achieve the desired end.
Valet stopped using leather and used a man-made material - it lasts quite well, but gets a bit too thin, so contact with the blade is sometimes problematical unless you introduce a lot of sag into the equation, then you run the risk of rounding the edge very soon.
If you have more than one strop at your disposal, you can always dust one lightly with green chrome oxide powder and use it to refresh the blade - it acts like a very fine blade. Keep the strop very taut and only do five - ten laps, then finish stropping on plain leather.
Regards,
Neil
