slooooow down cowboy. 
long tubes are not ideal for a turbo setup at all. They are used becasue people choose to use what they already have and go from there.
If you want the turbo positioned somewhere up inside the engine bay, you are talking 70" worth of headers, a crossover pipe from each collector, another 2-1 merger, and another 40"+ of tubing to feed the turbine. Thats A: expensive (3" 304ss is like $12 a foot, time for bends, time for welding, make a 2:1 merge…) and B: inefficient (velocity loss over length if dia isnt change to compensate). All the tight bends needed to physically fit the stuff in there will be like hitting brick walls when it comes to flow. Every bend adds restriction example: 180 degs of say 2" dia is like adding 12" of the same straight tubing to the run. not correct numbers you get the point.
Proper way is to get the exhaust gasses from the heads to the turbo as short as possible and keeping the velocity up to spin the turbine up fast.
the actually core of an intercooler is not in/out dependent. Hot side and cold side only is a goofy term used to say what side the inlet and outlet are on THAT PARTICULAR INSTALLATION. BUT. the end tanks can be formed in such a way that the flow leading up to, passing through and then entering and passing out of WOULD dictate the in/out for the installation. But if they are symmetric there is no difference.
You will no longer have a “true dual” exhausts with a single turbo setup. True duals are an equalized COMPLETE exhaust system left bank to right bank, with a X or H pipe in the middle to help balance it out. picture the turbo as being that X pipe. 2 heads feed into on turbo, the the turbo can have a down pipe split into 2 for duals… but performance wise there is not a reason to unless the volume is so great that you need say XXX Ci of volume inside the exhaust to not cause a restriction, and that tube would be spec’d to say 5" dia. 2, 3" dia tubes would then be ok to use because their internal volume, sum’d together would be = to or more than the 5" spec thats required.