Yikes! 18" . . . but great for the salt.
What oil filter are you going to run and where located? Incorporated into the tank?
I am not worried about the length as it wont effect the amount of torque the shaft will take. It makes the “springiness” of it change, but the cross section (limited by the spline section) is not changed. If gets very long, you get a different issue, but this isn’t all that long compared to the length of a half shaft which may carry 3-4 times as much torque. Plus, I think the CG issue is very important in car stability and we needed to shift the engine a little forward. You hit the nail on the head, its great for the salt.
One of the spots for the dry sump tank we have looked at is in between the trans axle and the bell-housing. Need to figure out a way to bring the two scavenge lines from the pump to the tank without aerating the oil? One idea I have is to snake it around like some NASCAR tanks. But its a lot harder on a square tank than on a NASCAR style round tank (if you want I can post a picture of what type of NASCAR tank I am talking about). Another problem we have is anticipating the future needs and trying to build for it. But I think a 5 gallon capacity tank should do the trick, a little overkill for the GMC.
I am not an engine guy, but having been around some dyno testing on filters and filter mounts I know if we don’t do this correctly we can loose HP, and on HP limited motors that can be huge. Any ideas let me know. Tony