[argonaut]

I have thought a lot about how best to add a high pressure fuel pump to the existing tank behind the seat so that I have a plan once I'm ready to swap the 8.1l in.

For fuel return I had the same conclusion as you did to simply braze a fitting onto the fuel sender and drop a tube down into the bottom of the tank.

For the pickup my main worry is fuel starvation at low fuel levels in the tank. I have heard that with no baffling, and a tank that is close to empty that you might starve the pickup tube during cornering. Maybe this is more of an issue with the under bed tanks than it is with the behind the seat tanks due to shape? I'm really not certain. But regardless I have given thought to adding some kind of small catch basin with weep holes to the bottom of the pickup tube on the sending unit. But I think it would be difficult to get such a thing back into the tank through the small shallow opening. Then I saw some kind of fuel mat product recently from Holley or one of the other aftermarket carb companies. I thought that might work to solve the sloshing and starvation problem. But I've not seen it used in a behind the seat tank.

I don't know whether your TPI needs a low or high pressure pump, but n I've had several pumps from bosch to trick flow recommended to me. I think all of these are rotary vane type non-positive displacement pumps that essentially use a liquid seal to be effective. As long as you can prime it with fuel, and locate it below the tank, then you shouldn't ever really have an issue with it sucking air and cavitation unless you run the tank dry. Sure it'll be a little louder but as long as you mount it using rubber pad or dampersomething then I think it'll work just fine.

Then high pressure supply and return lines are just a matter of typical fittings and adapters.

I'm curious to see what you end up doing since I don't know when I'll get around to actually doing my swap.