I've got the same truck, with a 351W in it.
(For anyone else reading this thread, the 347 is a common stroker size for a 302/5.0L).
Advantages to the 351W: No custom work needed to build it, it bolts right in.
Disadvantages to the 351W: Bit heavier, bit bigger (not an issue really for a full-sized Bronco), mileage sucks compared to a 302.
Advantages to a 347: More aftermarket intake manifolds avaiable than there are for a 351W, core engines are a lot more common, and if you want EFI, it's a lot easier to find an EFI 5.0L than it is to find an EFI 351W.
Disadvantages to a 347: Lots of custom work (read this as $$$).
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--C.J. Ford
1984 Bronco -- Daily Driver
1985 CJ-7 -- The Project
1996 Thunderbird -- The "Other Vehicle"