You didn't mention if the housing you're looking for is an 8" or 9", if it's an 8" they are easy enough to find so hold out for the '66 housing. If it's a 9", the '67 housing is about 1" wider on each side than the '66. The easiest way to compensate is with deeper backspacing on the rims. If you already have a set of rims that you want to keep you either need to have the housing narrowed or hold out for a '66. The '65-'66 9" housings are harder to find and therefore cost more than the later housings, but the added cost of rims or narrowing makes the overall cost about the same. If you're using stock width rims and tires it's possible they will clear the fender lip without changing anything.
If the '67 unit is a 9" and you have an 8" in it now you will have to get a new set of U-Bolts. The 8" set will be too narrow. The bottom shock mounts will also have to changed out. You could weld up the U=Bolt holes and redrill if your budget dictates.