What engine can I have?

Your 170 probably had a 170 cid engine. The 225 had the same bore but a 1" longer stroke. So in all actuality, same head, different (1/2" taller) block. These cars were available with a LA series V8 from the factory, so any LA small block will bolt in with factory parts (more or less). Big blocks dont fit so well, but it can be done.

V8 radiators are quite a bit bigger, and if you plan to keep the a/c, you need one. Later model 22" radiators should work, chose your water pump accordingly.