I'm not sure of the exact hieght differnece and I have to admit I'm not familier with marlin's front spring mount, but I would add at least 2" to the advertised spring lift to give a rough idea of how much higher you're going to be. Possibly even as much as 3" when compared to a stock SA truck. So, with 4" springs, expect at least 6" total lift.

You might consider a kit that has the least front drop spring mount, like the FROR kit (I believe) or a set of springs with less lift. There's some debate as far as how low you can go because the lesser arch of the IFS. Moving the axle forward helps some.

Also, I've heard that you don't mind living with almost no uptravel, you might be able to get away with around 3-4" of total lift. That's something I'm exploring right now as I look into dearching my fronts springs to lower my overall lift a bit. I'm not sure, but the lack of uptravel might not be that big of deal since the axle can still pivot off of the bumpstop and still give decent articulation.