Dang, I guess I haven't kept up with this thread... 9 pages sheesh.
I want to add my .02 real quick... In a remote rear twin setup, long tubes could possibly be beneficial. But in a kit where the turbos bolt on the stock manifolds in place of the cats, cast iron manifolds are best. Most turbo applications for street use have cast iron manifolds when the turbo bolts onto the manifold. Cast manifolds are incredibly durable at least in my experience with turbo diesels and gas motors. When the turbo is remote from the engine, the heat doesn't build up as badly sure, thinner long tubes are fine. Also you have to be running an internal waste gate on these so the heat is going to go up from that (since you are sending highly pressurized highly heated air through the turbo because it has the waste gate built in). I would think you want to have oil piped right in with a pretty good oil cooler for the motor and turbo to take the extra stress there. I mean yea heat is good in a turbo but you have to control it. if you have an oiled turbo it is cooled from the oil under high load situations and helps a lot. I get you are trying to build an economic kit here. I totally support it. But if I was going to do something like this (granted I'm not) it would have to be an engine oiled turbo just for day to day reliability like my last car was. I get it if you are just going to run a 1/4 mile... No problem with turbos that have internal lubrication there. They only deal with heat for a few seconds. But let's say I want to drive from my house to Vegas with a set of twins on the V. That about 5 hours each way, up a rather large grade for several hours and knowing me, I would be in boost for the better part of 2 hours constantly going up into the mountains between LA and Vegas. I'm not saying that internally oiled turbos would not be able to take it, I'm just saying, for piece of mind, I think having oil pumped in, constantly lubricating and cooling the turbo would co a long way to increasing longevity. The internal/external oiled turbo discussion is like the camshaft lobe discussions. certain ones are hard on valve train but they sound good and make lots of power but there are threads everywhere about how they fail because people spec these gnarly drag cams for daily street use. Its the same with turbos gotta spec the right ones.