Mystery compressor

As Darter6 mentioned what year 318 matters. 69 and earlier used a single drive belt on the A/C compressor. 1970 and up used a dual belt system that also drove the alternator. The compressor you have would work on a 70 and up 318. You will have to find the right compressor mounting bracket and supports. Also, you will need to get the crankshaft pulley and all the other pulleys worked out for an A/C setup. You will also need to find the specific A/C refrigerant lines for a 66. All in all, you might find it easier to use a newer retrofit kit from a company like Classic Air. Otherwise, you're going to be doing a lot of searching for original system parts.