Regarding the transfer case, we have never used one. Marlin says he would assume it to be just as strong as the non-center differential t/case, however not all Tundras have this feature. It may be a more rare occurrence that needs furtherer investigation.
another newbie question, what is the shift pattern for the dual case, is it just the 1:1 and then shift down to 2.28:1 
That is correct. Low-Neutral-High. High range is 1:1 on all of our products, and low range is 2:28 (default) or our optional Total-Spline 4.70:1 gearing. A/A 4.00 and 4.97:1 gear ratios are also available however I would highly recommend against using them with a V8 due to their weaker design.
also, what are the spline counts that are used with this setup?
All of the spline counts here are 23-spline. 23-spline Tundra Auto output, 23-spline Marlin Crawl Box input, 23-spline Marlin Crawl Box coupler output, 23-spline Tundra Chain Drive t/case.
Regards,
BigMike
