Dana in a dart

There was enough threads on my perches that I could space them back 3/8 inch, which allowed 275/60-15s (~28tall)
Had there not been, I would have just knocked them out, installed longer bolts, and fabbed up a thicker spacer. After that I wouldda looked at the shackle angles and fixed that as might have been required. But 3/8 was ok.

But I like your idea. Just make be sure to fill the previous holes so that the thing stays where you put it. Be advised tho, that as you lengthen the front segment, other things can happen...... like wheelhop... I hate that.
BTW;
Super nice nostalgia wheels; I have that style on my 68 Barracuda, but with a 4.5bs.