Hit 330x7 front squat a couple weeks ago w/ belt, at 205#. Decent strength, but nothing crazy.
I just do a bunch of front squats without a belt: 4x5, followed by an AMRAP set. I also do them later in the week much heavier with a belt, 3x3 (occasionally AMRAP)
I also do beltless deadlifts.
Just keep plugging away, IMHO.
If I was going to do ab work, I'd use the ab roller & heavy side bends.
Are you sure abs are the weak point? Leaning forward can happen because your quads are weak, and your body wants to shift into a position to use your hamstrings/back. If you've ever used knee wraps and experienced the ability to stay more upright with them on, that's why -- it assists your quads.