Hi Viking;

Since I'm both a plumber (held a master's license for over 30 years) and an engineer (at least by training), I think I can answer.

If your all your lines are joined above ground, you absolutely can solve your flow problem by connecting them in a 2" or 3" header. Just avoid any bullhead-T connections, where you have two flow streams colliding head-on.

A couple of corrections, though.

+ For virtually all centrifugal pumps, the max load occurs in the low pressure / high flow zone, not in the high pressure / low flow zone of the curve.

+ High efficiency pool circulation is achieved with balanced piping that is oversized, compared to what's standard and matched to a low max head pump. In practice this combo is available via a slightly oversized pump that has a two speed motor. Typical centrifugal characteristics commonly result in 1/2 of the high speed (3600 rpm) flow at low speed (1800 rpm) , but only 1/6 of the load.

+ Some elements of your hydraulic analysis aren't quite right, but as they say, "you're close enough for government work".

+ I've never met a pool builder with even a vague understanding of how to calculate flows in a pool system. I know there are some -- I've just never met one.
[ In fact, most of the engineers I've seen involved in projects that included pools apparently could not do so, either. Given that it's all a matter of applying the empirical Hazen-Williams formula (which you can load into a spread sheet), and combining it with data supplied by most pipe and gear manufacturers, it's obviously tech that's well within reach of any engineer. It's just that most engineers seem to work in environments where they design only by the supplied cookbook . . . and there's no "Handbook of Swimming Pool Design" worthy of the name. ]

Good luck!

Ben