01 crew cab 4x4 s10

ZR2 is an off road package that includes some changes to the frame width causing motor mounts to be in a different location than a standard 4wd.
The ZR5 is a bling package. Nothing in the package is for off road use. No difference in the frame from any other standard 4wd. You just need S10 4wd LS motor mounts. The ZR2 package was never put on the crew cabs.
I think you'll find keeping your present transfer case a lot less trouble than adapting the S10 to accept a full size truck TC. The oil pan is going to be expensive for fitting an LS in with the front differential. The Milodon 31083 pan and oil pump pickup tube is >$600 not including the remote filter kit. I believe there are few cheaper ones out there, but the oil pan and pump tube are no place to be pinching pennies.
An LS into a 4wd crewcab is a big, pricey, time consuming swap. Probably $6K ad 6 months bare minimum. I have an 02 crewcab and yes they are doggey because of their weight (4000 lbs +). If I do swap mine I'm going with a SBC L31 to save both time and money since it will never be fast.

Seriously doubt a small drop in the location of the front differential will help any.
If I knew Photoshop better I would have made them the same size and overlayed them.
The problem is forward to rearward location of the differential and the fact LS engines have a deeper bearing cap depth for the horizontal main cap bolts. That's even an issue in the 2wd trucks. The older 1st gen SBC could use a stock pan in a 2wd swap.
4wd's always needed swap pans. Back in the day when the pans were tin you could make your own by sectioning a 4.3 4wd pan rear half and a V8 front half.
You can cut and mod the aluminum one if you are equipped to weld aluminum. It does take a bunch of welds, tho.

I say do a Zr2 frame swap. It's not terribly difficult i have a thread on here. The rear cab mounts need to be swapped, build some front bed mounts, and use the crew cab fuel tank with the ZR2 skid plate. If you have the ability, i say go for it. Also, as others will mention, look at the frames near the lower control arms, not uncommon to have stress cracks. Also, i am swapping a 5.3/nv3500/ np231 t-case. I have an RC 2.5" lift, and with cpw motor mounts, i believe that an h3 hummer pan might work. I am using the stock pan, so i had to cut, but not as much as i could have had to if not for the diff drop. You would also drop the pan more on the rear mount, which could help with the pan also.

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