Ok, I answered the question asked, but there is a lot of totally unrelated information than whether a BRM head can be used to do a BEW job. The most direct answer is NO.
The BEW is the only TDI engine I know that the piston tops are flat, which by the way, means a much better swirl chamber effect. All other engines that are TDI's that I know have valve protrusion for the valves and valve recesses in the pistons. So, if you put a BRM/ BHW head onto a BEW block, you are going to crush the valves into the pistons.
And yes, the ONLY difference between the BRM and BHW is the size of the hole in the head gasket to allow for the BHW's larger pistons. Keep in mind, the head gasket thickness is to compensate for the height of the pistons, not the head and the BHW pistons have to fit through the head gasket, therefore, the larger 81.5mm hole instead of the BRM's 80mm (?) hole.
Changing to the BEW valves will do nothing to move the valve seats. The only difference with the BEW valves is that they are .5mm shorter than the BRM/ BHW valves. So, save your time getting another valve from BEW. If you use the BRM valves, the stem height cannot be modified enough by trimming the stems. You will be into the top of the cotters. If you don't get the valve stem height correct, by using a BRM valve, the cam followers are overly compressed.
The other difference with the BEW is that the intake port is split. That is to match with a butterfly on the manifold that closes off the short side of the port. The intent is that in low speed/ low volume air flow that the swirl chamber effect would be improved. I think it's a lot of hokey stuff to make that happen, but it does seem to work, so what the heck.
The pulley hubs are different between the BRM as they don't have split 'finger' for the piston identifier. The BRM have a solid bar, as the BHW/ BEW have the pair of fingers. That cam position sensor does a very cool thing to note which piston it first 'sees' and tells the ECU to fire the next compression stroke in order. That makes the PD motor, properly set up a 'One-Two- GO!' engine.
That is a bit of TMI, but I hope it's clear enough. I've seen the innocent idiot put a BRM head on the BEW block with a very short life, crushed pistons and bent valves. If you change the valve to a recessed valve in a BRM head, you will also have to change the valve to the shorter BEW.
Last thing; except for the valve seats being recessed into the head on the BEW, the head itself for all of the 4 cylinder PD motors is exactly the same casting.
Keystoner, if this is at all confusing, feel free to give me a call or PM me.