modulator is on pass. side on a 400 and rear on a 350.
A 700r4 built right is better than a 350 . it has a lower 1st gear and overdrive .
I'll disagree that a 700r4 is better than a 350 even properly built. Even properly built, the Th350 is more durable. You are correct though about the lower first gear, but that also creates another disadvantage. There is a wide gap between 1st and 2nd on the 700r4 cuz of the lower first gear.
Bottom line, it all depends on the what you intend to use the vehicle for. I'd only go with a 700r4 if I was making a grocery gitter and daily commuter where mpg is important, and I'd only do that if I were running 3.73 gear or lower to take some of the strain off the 700r4, and still have the OD to compensate for it. So actaully, the decision needs to be based on, what's the vehicle main purpose, whether it be a weekend cruiser, street/strip truck, daily driver, or basic work truck for hauling the ATV's around or mowing lawns on the weekends, then what gear ratio does the truck have in the rear, and are you willing to change it to be a good match with the trans.
