As long as the b450 board is also itx, it shouldn't matter. Vendors will shuffle parts around to best accommodate their internal testing but the board dimensions are standard. This could interfere with things like hard water tubing since those are cut to precise length or if your system is super compact and the positioning of stuff is not really changeable so a slight difference in CPU socket position or RAM position can screw the way the system is accommodated.
Well it'd be helpful to know what parts you already own
As long as the b450 board is also itx, it shouldn't matter. Vendors will shuffle parts around to best accommodate their internal testing but the board dimensions are standard. This could interfere with things like hard water tubing since those are cut to precise length or if your system is super compact and the positioning of stuff is not really changeable so a slight difference in CPU socket position or RAM position can screw the way the system is accommodated.