I'll weigh in. I had a similar dilemma few years ago desperately needing a deeper low ratio.
You just aren't gonna gain a 7:17 and retain your current wheelbase or 27" rear shaft
There's just no such thing as a 7:17 without doubling or different axles
That being said, you can run a lomax in the 205. That'll get you 3:1
You can run a rubicon case that will get you 4:1 and with I'm assuming a TBI you'll be fine until you beat it too hard and even then they handle some pretty dang good abuse. But keep in mind the rubicon case is not a direct swap, it has a 23 spline input and your TH350 has a 27 spline GM output, if I'm remembering correctly
Excluding the atlas like you said, you can combine one of those 2 with 5:13s, which I wouldn't go any deeper if you want axles to live and get you pretty decent ratio. You still aren't even knocking on the door of what 7:17 feels like. I don't even know what size tires you run.
Doubling is in my opinion the best way to go. You get multiple gearing options and you may even get away with not swapping gears if you like the lowest ratio which is 5.3:1 without the lomax or 8:1 with it.
The crawl box is a solid 10" on to the tail of your housing
No matter what you aren't gonna gain anymore than 4:1 without drivetrain length
I run a NWF ecobox in front of a 231 with a slip yoke eliminator. Grabs me 7.4:1 to the axles with 5:13s. 60 front and 14 rear. Oh and with 1330 joint front and 1310 joints at the tcase outputs
I run 42" reds, it was one of the best if not THE best upgrades I have made.
Post up what you do. I'm curious
