440 RB engine, new transmission,new bolt pattern...

yeah, it is not "needed" but it may, may, make things easier in the long haul

US indy still makes SBP wheels in several sizes BUT definitely easier to find wheels in BBP, specially where you're at
(just curious, what part of Belgium are you from?)

lets start on the back, what rear end do you have now?

if that is up to the job, you can get either a Kelsey Hayes set up for the front, or a scare bird conversion kit
both of those will allow you to keep the SBP

if the rear end needs to be replaced anyway, might as well find one with the BBP and swap the front to match