I would suggest that you avoid the lever setup. You typically don''t have the range of adjustment that a backstay adjuster needs and the custom fabrication of a lever able to withstand backstay forces would be quite expensive.
Probably the easiest set-up for a boat without a split backstay would be a cascading set up where you have a single wire block hung on the end of the backstay. (The backstay will need to be shortened.) A wirerope then runs from a trianglar plate at the chainplate at the deck thru the block on the backstay. Depending on the size of the boat there would typically be another wire block hung on the end of the first wire rope and another wire rope that runs through that block and has a thimble in the end. Again depending on the size of boat there would typcially be a 4:1 up to a 6:1 purchase. This combo results in a 16:1 to 24:1 overall purchase. (On really big boats there may actually be a third cascade resulting in 32:1 to 48:1 purchase, but for example, my prior boat, a Laser 28, had a 16:1 and my Farr 38 has 20:1 purchase on their backstay adjusters which seem adequate.)
Garhauerer seems to have the best prices on the kind of low friction blocks that you are looking for.