I bought a 3/8 sending unit. Wrong Unit?

There is no difference between throttle linkage on a carb for a 170 vs. 225. The '60-'66 slant-6 A-bodies (except '65-'66 with factory A/C) use a box-shaped throttle lever with a rubber bushing snapped into it; the car's rotating throttle rod snaps into this bushing. The '62-up slant-6 B-bodies, the '65-'66 slant-6 A-bodies with factory air, and all '67-up cars use a cable-type throttle hookup without the rotating rod. None of the numbers you've posted identifies the carburetor; those are all casting numbers. To ID the carb, you'd need the number off the aluminum tag originally secured to one of the front (short) bowl screws. These are usually missing on carbs that have been "remanufactured". Fortunately, virtually all the Carter BBS carbs use the same kit so you can refer to Carter number 3676s. The "s" is not always listed in aftermarket kit listings; disregard it -- there's no significance to it (that is, there's no difference between "3676" and "3676s". Tough to find good quality carb kits any more. Good ones with a better, updated inlet needle and seat design come from www.daytonaparts.com , but -- like all the other mass-market kits on the market nowtimes -- it won't come with a proper float gauge, which is a major problem; the stupid little piece of paper ruler they include is useless. I'm working on having some proper float gauges made available, but they're not here yet.

Pushing 5/16" hose onto a 3/8" nipple is a poor idea. The hose is not meant to stretch that much and you are talking about making a connection to carry an explosively flammable liquid. Do the job right return the incorrect sender and get the correct one.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download. Tune-up parts and technique suggestions in this thread.