I had the samething on my '87 and '94. I was told the first one (smaller) is a resonator and the second one is the cataltic converter. The mechanic that changed the one out on the '87 said that and the new one that went on only had the one combined (assuming) into the one cat. BTW after the new one went on, a lot better take off (seat of pants) to the truck. But made my own exhaust choice of exhaust about 1 year before cat change and that helpped too. Put a 351 muffler on (single in, dual out) and added the dual tails with chrome tips. Nice look and better take off, might think of that combo instead of true duals. Only cost around $250 at a local muffler shop.
Have Fun & Keep on Truckin'
1994 F-150 XLT Supercab, Long Box, 302 EFI, Automatic, Royal Blue in and out, Captain Chairs. Chrome Rims 15x8's, Michelin LTX M/S 105S 235/75R15 (Summer), OEM Aluminum Rims 15x8's, Michelin LTX M/S 108S (Winter), Lightly Tinted, Soft Tonneau Cover, Ford Receiver Hitch Cover & Lock, Alpine CDM-7829 Head Unit, PPI 4800 Amplifier, Kicker 10" Solo Baric Sub with Custom Box and Kicker Impulse 6.5 Mid & Tweets.