Hmm what a coincidence. Just did this job myself on the 87 240 (230K or so), with the same parts from FCP groton. Yup, that ring did NOT want to go back on. That was REALLY tight!!! I hammered for like half an hour and lubed everything up with Neverseize. Fortunately I know it's all new in there and won't need to be back out again (Unfortunately, the car still stalls at full throttle, go figure! GRRRR!)
I did seriously consider reusing the old gasket and would have saved myself endless aggravation. IT is ESSENTIAL to get the whole ring/nut area clean clean clean. Mine had all sorts of rust grit and old undercoating in it. I also made sure I didn't bend the locking ears on the tank (I hadn't).
Anyway, you REALLY should go get the sock. I worried about losing mine while doing this- it's a tough piece to fit on the pump. I would get a telescoping magnetic tool from Sears- I've got one with a 3-inch magnet on a pivot on the end, it lets you sweep around to find things. The steel ring on the sock should be easy to grab. Then reinstall it to the pump and um, don't lose it!

Good luck! (Aint that just a great job?)
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Rob Bareiss, New London CT ::: '86 244DL- 215K, 87 244DL- 230K, 88 744GLE- 198K, 91 244 180K