I also have Rally II's in a 15" Stock offset and have 225/50/15's all the way around with no problems on my 67 drop top.
And have some room to spare. I know many who run a 235 or 245 in the rear on 67/68's and are ok.
I think it would be a good idea if you ran say a 225 or 215 in the front if you are at all worried. I've always liked the 50 series just for the fact that it has a stiffer sidewall and usually is more responsive in cornering... even though I don't drive as hard as I used to... (And haven't had a ticket in many years) Hmmm? I wonder if there is something to that?... Naw....
If you were going up to a 17" or 18" wheel, I'd sweat the details, and tripple check the specs, but on a 15" Rally II, you should be just fine!
Show us some before and after pix when you get them on!