I'm working on the specifics but it's looking like all you really need are the cases (covers would be nice) and the head cover and a few shifter shaft parts and oil pump.
Vertical head fits, jugs fit, looks like the gearbox fits, clutch fits, crank fits (have to use sloper alt/timing plate or make your own). Vert uses different shift ratchet, superior in my opinion, vert shift shaft is longer than sloper but fits (should be easy enough to weld a vert shaft on a sloper ratchet). CB160 left side engine cover will work on a the sloper 175 if you bore out the shifter shaft hole and press in a needle bearing. Right side cb160 might work too but I haven't checked.
From what I can tell the whole vert. 175 shifter ratchet can be used with a tiny bit of work to the right side of the crankcase to add a little stop pin that the vert. uses that the sloper doesn't have. Go here: http://www.jrbranson.com/showandtell2.htm
to see some pics and details of the sloper fiver, versus the vert. fiver.