In a word, Yes.
I think that I've purchased and sold a couple of 5x7 backs for the Sinar system. But, one will need to look for a Sinar P 5x7 back, versus the F series. I believe I've seen references to a 5x7 F assembly in Sinar literature, but I've not seen one personally, nor on eBay. And, I've purchased and sole quite a lot of Sinar equipment.
The 5x7 format frame fits the Sinar P 4x5 standard, in case one finds just the 5x7 format frame. Because of the effective unavailability of a rear F2 5x7 back, a fully equipped, Sinar 5x7, even with an F2 front, tends to be a bit heavy. It's not that difficult to find both 5x7 accordion bellows and 5x7 bag bellows for wider lenses.
I recommend a 4x5 F2 front standard with the longer risers designed for use with Sinar 8x10 equipment, in order to have sufficient rise for the taller 5x7 P back. These F2 front standards can also be found with independent shift, tilt and swing. (Separate locking levers for each.) 4x5 reduction backs exist for the 5x7 format frame, so that one can photograph using either 4x5 or 5x7 film with a 5x7 camera.