Unfortunately, a 4x4 under a 8" beam is not the same as a 12" beam.
That involves keeping the existing beam? That beam is only
30% as stiff as the 11.25" LVL. You would three of them.
That existing 4x8 doesn't buy you any height reduction. Using 3 4x8 is not the same as using a single 4x24. It's very different. The existing 4x8 will get you down to a 3.5" x 10" LVL, but it's 9.25" or 11.25". There is no 10" LVL.
Do you have any other questions for me on this question? If you could rate my answer, I would appreciate it.