I would try the duel sump 5.0 pan first. Easier to come by, probably cheaper. The Bronco pan has an odd looking recess on the left side to clear the front axle, guess it doesn't look odd on a Bronco but it does on anything else.
If a Bronco pan will work on the 351W, and I do not know that it will, but you seem to think so, I cannot imagine the 5.0 pan wouldn't fit the 351W as well. I did use a 5.0 pan on a 289 last year and the only issues were it was necessary to use the later oil pump (a little shorter) and had to make provisions for a dip stick in the pan's rear sump. Ray
I am pretty sure it won't work as the 351 W has bigger mains. All the manufacturers list them under different part #'s. I got a 351W pan from Summit that worked great in my application.
The 351W and 302 pans don't interchange, the pan rail configuration on the block is different. Another issue is the 5.0 rear-sump pans don't have a provision for a dipstick as the block is drilled for it. The rear-sump 351W pan comes with the dipstick. The 351W wasn't installed in any Bronco until 1982, so that's where you need to start looking ('82 though end of production in '96). Same years 4WD 351W-powered trucks will have the same pan, and will be easier to find. The rear-sump pan was also used in vans (roughly the same years), another choice. If you can find one, the 351W rear-sump pan used in the very limited-production '93 'Cobra R' Mustang is the best choice. This was offered as an aftermarket 'swap pan' by Ford Motorsport (used as well by Mustang 'tuners' like Saleen and Roush to install the 351W into Fox-body Mustangs) for a few years but is long discontinued.
The early 5.0 Fox mustangs had a dipstick in the pan. The pan had a riveted or bolted and gas keyed dipstick adaptor in the side. Later cars use the drilled front cover. The 351 and 302 pans are not interchangeable, as discussed. I'm not sure, but I think the late 70s, early 80s full sized 351 W in some full sized police cars had a rear dump pan also. They're pretty rare, as most were 302 equipped.
Opp's, missed that it was a 351W. I just put a duel sump pan on a 351 I've swapped into an ot car, bought it with the pickup tube from Summit, I think it was a Ford Motorsport part so not sure they been discontinued. Still should be several options to get a pan you need.
a hunnert years ago, I got mine from a bronco specialties shop called k-bar-s out of nevada. I don't think they are still in business. a 5.0/302 pan will not fit the 351. search 351w engine swap in either 66-77 broncos or fox body mustangs.