This is a shot in the dark since not a whole lot of people have done this swap, but I need a driveshaft for a 99+ Shortbed, single cab, silverado/sierra with a t-400 yoke and an 8.6 yoke.

 

wow it might be your luckey day. haha I may be swapping back to a 4l80 but wont know for the next few days till i get it all worked out first. but it looks like i am going to be doing the swap. I will keep you in mind. I have a mark williams chromoly driveshaft that cost me $900. it has the 1350 U-joints and i have a 9" so i am not too sure how that would work with the stock 10 bolt

 

My stock d-shaft from my TH350/10-bolt (8.5) is sitting in the bed of my truck. Waiting to get a custom d-shaft made with a longer length.

 

I thought about pm'ing you, but I remembered you had a 9". I'm not sure the length would be right, but I'd venture to say it'd have to be damn close. Even if it isn't right, I'd still be interested because a 9" is probably in my near future at this point. Let me know if/when you decide.