A locker on the GM IFS is looking for disaster I think. The first time a wheel spins and the diff locks, it'll most certainly destroy the half shaft. The IFS setup is not robust. Which is probably why nobody makes a locker for it.
If you are really going to be doing driving where you need a front locker, go with the Ford. Besides the solid front axle, you get a much more robust frame/chassis and stronger transmission. And other goodies for off-roading like a power steering cooler, tighter turning radius, and better ground clearance.
SalemKroger:Over the years we've found that Ford 4x4 vans and 4x4 trucks have a better engine selection and most importantly, a stronger frame than other manufacturers.
Also notice SMB and QuadVan only do Fords, and the majority of the 4x4 members on here have Fords.
Quigley will install a Ford solid axle setup into the GM van, but then you could run into future service issues having a Frankenvan like that, and I'm guessing they cannot do it on the new models with StabilTrac.