Notice in that pic, the flexible tubing is probably 4" in dia and necks down to 3" at the MAF. If you use flex tube, be certain it is 4" when the MAF is 3", that will greatly reduce any restriction in the flex tubing.
I used aluminum dyer flex 4" tubing on my truck as I could not find any other type of flex tubing that would work on my TPI motor to get the intake filter out from behind the hot radiator air. Worked great and looked pretty sharp too and would not collapse.
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But, for the TR, flex tubing at that location can be tricky because there are sone sharp edges going out of the body behind the headlight that will easly puncture the flex tubing.
Best bet, either get Mark's setup, or go to the local Freightliner/big rig store and buy some 90 and 45 degree exhaust elbows that are 4" dia and some sewer pipe connectors from HD.