The old Meg's "APC" was different than the old "APC+". IMO, the APC+ was a more versatile product.
I think the APC which contained Butyl, has been dropped from the line.
The new D-10101 All Purpose Cleaner appears to be the replacement for APC+.
I haven't used the new stuff, but I really like the old APC+. Hopefully the new product will be just as good.
I purchase mine through a body shop supply store, but any Meg's distributor can order it for you. Getting some of them to do it might not be that easy.
I'd avoid it if at all possible -- or maybe apply it using a shop rag or something that isn't going to have the overspray getting all over the wheels and surrounding areas. Most whitewalls aren't usually going to be THAT dirty.
I wouldn't use it at such a dilution for regular cleaning, but as a one-off thing for a car that hasn't had its tires touched for months it's not so bad.