The main "plus" from a longer rod is that you cut the compression height of the piston way down.
When working with a 3.5" stroke in an FE, the tall deck height makes for a very tall piston. Even with a small diameter, you're looking at a pretty heavy slug. A 6.700-6.800-7.100 rod will help that tremendously. Even with a 7.100" rod on a 10.150" deck, you're still at a 1.300" compression height. Obviously, you need a BBC rod journal, which isn't a deal breaker, but it does add a good bit of cost to the machining bill. You either widen the journal in addition to turning the diameter down, or you run a narrowed rod and bearing. Either option is not cheap.
The caveat to this is where you have a very large intake port in relation to the displacement of the engine. For instance, a Boss 302 engine will benefit from a shorter rod as it keeps dwell time down, which in turn keeps the intake charge moving. With the heads that will fit on a small bore FE, you generally won't have that issue though, unless the heads are hogged.
If I were building a hipo 352, I would go the 7.100" rod route....
I'm also not convinced that a longer rod won't make more torque in certain situations. I have built a few engines where I was rewarded with a little more torque than I was expecting. One instance was a road race 289, in which I used a steel crank, had the rod journals turned down to SBC size, used a Molnar 5.700" SBC rod that had been narrowed considerably (by about .110") and then used a GM V6 rod bearing. Even with a 7000-7500 rpm horsepower peak, it still made 390 lb-ft of torque....a ton of torque out of a little engine.
