Not sure exactly what you mean by reinforced, I think most people cut it so that the upper lip is still intact then just close it off with some sheet metal where they cut it.
All the ones I've seen have just had the stock posts with out re enforcement and the have held up over time. My room mate had one that had been done for over 10 yrs and it was fine. You could probably plate the backside of the pillar in the area that is covered by the interior trim to beef it up a bit and finish the back ot the same time.
how heavy is your windshield, Most windows dont weigh more than 35lbs....if 35lbs of force is going to collapse the window posts, along with the inners, I'd be incredibly supprised.