Move ISG to t0... give isg a small AT direct fire mode, adjust price.
Miragefla tried that a while back. He gave the leIG a 7.5cm "hollow charge" ability for 30 munitions that did 80 damage, 50 range, direct-fire. Our testing concluded that it was inadequate as an AT tool and the idea as scrapped; hence you have the 270MP leIG you have now.
Personally, I would put the IR Halftrack into Special Operations (replacing artillery flares), and give the Battlegrouppe HQ the Sdkfz. 250 Halftrack. Start with a clone of the Ostheer version and adjust from there.
Because the Panzerfusiliers were reworked, I do not believe that giving T1 an AT squad would be the best course of action (as the roles would overlap).