Converting 68 Valiant Rear to use 15" wheels

Hello! I've been looking at buying a 68 valiant (slant 6, 225 cu in version, if that matters). The car comes with a kit to convert the front to disc brakes and after I'll have it all installed, I'll have to use 15" wheels. This is all fine and good but I'm not quite sure what I'm going to do for the rear. I've done some searching but am still a bit confused so I just wanna make sure I'm thinking straight. From this one thread in particular, it seems like I have to either, A) buy a whole new rear axle assembly, B) run "lower profile tires for the front and/or taller 13's in the rear". While it may be overkill for just a (hopefully eventual) daily driver, if I got a rear disc break conversion kit, like this one I ended up coming across, I think I should be able to run 15in wheels with a 4.500/4.750 in bolt pattern, at least according to the sales page for this kit and I wouldn't have to source another rear axle assembly or shorten my drive shaft.
Aside from this being a bit overkill, is there a reason I should steer clear of this route?
Sorry if this isn't in the right place to post this, I'm new to this forum.