Back to the question !!!!!
".........The reason I'm asking is that a friend has a tri-power setup that has the carbs all on the same plane. I know that other tri-power setups have the carbs at different planes because of engine tilt. My Galaxie has the Thunderbird engine in it and I don't want to buy the wrong intake....."
If you want a Tri-Power and you are not concerned about all that numbers matching/correct/not correct BS, grab it and bolt it on. The 406 Tri-power was different than the 390 62-3 T Bird unit primarly in HEIGHT. The T Bird intake will fit unter the hood of your Galaxie, but the the 406 unit will not let the Thunder-bird hood close.
The 406 will make a little bit more HP, based mostly on the high rise design, but not that much.
Yes you engine sits at a slight tilt, but not enough to matter. (Do you think the makers of the run of the mill aftermarket manifolds really take the eninge tilt into consideration?). JMO, but I believe the tilt on the 406 intakes was mainly for astetics.
Just for general information in the early 60s (at least through 64) Ford slapped Thunderbird valve covers on all their 390 engines no matter what car they were put in. PURE ADVERTISING.