I've been asked that question many, many times. I've measured the 1 7/8" manifolds and came to the conclusion that the most I could comfortably remove is about 1/16"- 1/8" which is hardly worth the trouble. So maybe out to 2" max but I couldn't guarantee it since I've never tested one. I'm sure some material can be removed but the big difference is in the casting thickness. The 360 magnum manifolds are over-engineered so there's plenty of material in this area.
