i also have a 66 SS, congrats on your new nova. here is a link that you will find what your looking for. there's alot to read an you might be more confused after you read it all. size all depends if you have original drums an axle in the rear an what is in front original stock drums or disks all will change what back space you need.
i have drums in the rear 235 60 15 with 4 1/8th back space, 4 3/8th BS would be better. they are tight maybe a 1/2'' from inner fender lip. front i have early 70's disks. front is 205 70 14'' with a 4 3/8'' BS. no rub an i can turn lock to lock with no rub. i first had 14's with a 3 3/4'' back space an they rubbed bad with the 205's. also the wheels front an back are ralley wheels. https://www.stevesnovasite.com/threads/2nd-generation-66-67-wheel-and-tire-fitment.174591/
Thanks Red Rider for the info. I have been looking over Tire and Wheel specs. I rolled out a 225 60 15 , 7 inch rally from my Camaro and that fits no problem on the rear of the Nova. That's with a 4 1/4 inch backspace. I still had a good inch to the leaf spring on the inside. I can see where the 235 60 15 would not be a problem this leads me to believe where in several articles I read that 4.50 is a good medium backspace. The same 225 60s on the front of the Nova did rub just a tick on the very lower front fender molding.
yes i'd think the 225 would be tight an rub on corners. but your talking a 60 series an i've got 70's in front. also dia. plays a big part also from 60 to 70. an the 225 in rear with a 4 1/2'' b.s. would fit good. as the 235's in my rear i have to let the air out to install. to tight from top of the drum to inside fender lip. let me know how you make out. i'd also like to have a set of cragar SS to change the look some times on my 66.