Notice the shape of the 235hp exhaust baffle plate assembly between the cylinder heads...... the manner in which it protrudes outward.
Notice that the 150hp baffle plate assembly is flat.
The adapter plate on which the 235hp powerhead sits is of a different design so as to accept that extended baffle plate assembly of the 235hp model.
You could use either powerhead you wish to but only if you incorporate the proper adapter plate...... or the entire exhaust housing (housing between the powerhead and lower unit) to match the powerhead you intend to use.
My previous answer pertained to simply moving a 235hp powerhead to a 150hp adapter plate (or vice versa) which obviously would work.
