Tank Selector Unit

I know that there is a high and low pressure unit availible for these older trucks. For upgrading to intank pumps, I understand the high pressure TSU must be used.

I am however considering using an inline Walbro 255 pump mounted on the frame rail, connected directly to a vette filter/regulator. I like the idea of having the pump accessible in case of failure without having to drop a tank, and from what I read, the new inlines are almost as quite as the in tanks.

Now in doing so, the return line would be plumbed back through the TSU. Would there be any pressure whatsoever in the return line that might effect a low pressure tank selector unit? I figure there may be some, since the supply line is 3/8ths, and return is only 5/16ths. But since there is no resistance in the tank, perhaps there would be no pressure buildup in the return. I dunno, thoughts?