rb tunnel ram on a b motor

I think your going to have some difficulty with narrowing 2 inches out of that without radically altering the runner shape/transition. That’s not going to matter as much with LPG, but you’ll still want to do it in a way to equalize the runner shape, length, and angle as much as possible. What brand of manifold is it? I don’t think it would be impossible to do, but it would definitely be challenging.