well i thought i try and give you my take on this as from what i have seen so far the installs are far to complicated and with a little thought can be carried out using gen bmw parts which is allways good IMO, i did use this site as this guy was so nearly there and it may help you further more
so here goes
PARTS YOU WILL NEED
1 X M50 Vacum hose and connector( this is the connecting hose to the back of the manifold.
1 x T section 22mm connector( you can get these from any garden centre's or you can use a copper 22mm T section from you plumbers)
1 x M50 ICV hose ( hose used to run up to your maf boot)
7 x 25mm sir clips
1 x streight connector and a small section off hose ( size to come)
6 x manifold gasket + if you use the 328 throttle body 2 x gaskets, 1 for the manifold and i for the body, i'll explain later in the thread
1 x replacement ICV hose to maf boot
Ok so lets start
remove the fuel injector cover, unplug the O2 sensors, unbolt the fuel rail and carefully pry the injectors together with the fuel rail out of the manifold. Next, remove your air box, intake boot and MAF. Carefully unclip the ASC+T throttle cable from the secondary throttle body. Remove your alternator cooling duct and unplug the throttle position sensor as well as the purge valve (on some earlier cars the purge valve is mounted to the shock tower so just leave it alone). Unbolt your throttle body and lay it to the side. Now unbolt the bracket that holds the idle control valve and the oil dipstick tube. Pop the idle control valve out of the manifold, unbolt your oil separator and start unbolting the intake manifold.
Once the manifold is out of the way cut the zip ties that hold the wiring harness to the bracket on the engine block. Remove the bracket and install an OBD-I bracket part number 12-52-1-724-264 in its place. OBD-I bracket will need to be slightly modified. A hole at the bottom of it will need to be enlarged to 8mm and at the top it will need to be bent slightly to clear the bracket near the back of the engine. You will also have to loosen the front knock sensor and turn it slightly to clear the bracket. Make sure you torque the knock sensor back to specs. Once the OBD-I bracket is installed start attaching the wiring harness to it with zip ties. The reason I used an OBD-I bracket is because it has a holder for the idle control valve on it.
Bolt up two OBD-I manifold brackets to your block. Part numbers for the brackets are 11-61-1-735-265 and 11-61-1-738-759. Please note how the new brackets mount to different locations on the block. Front bracket mounts to a threaded hole in the block right behind the engine mount and the rear bracket mounts to an engine mount itself.
Now it is time to sort out all of the hoses. I used an OBD-I hose 13-41-1-738-185, and installed a T-fitting into it. Your oil separator and ICV will connect to this vacuum source. The air pump control valve hose will connect directly to the connector 11-61-1-738-929 that clips into the back of the manifold. To connect the oil separator to the T-fitting I used an idle control valve hose 13-41-1-435-781. This hose is the one that connects the idle control valve to the INTAKE BOOT, I simply cut it into several sections, the u bend section io used to connect to the oil separator and the streight section i used to connect to the ICV, so thats the main hoses done, all that is left is to fit a length of extension hose to the vacum manifold connector and then if you look you will see a vacum sorce no the underside off the manifold connect your fuel rail vacum hose to this and then all that is left is the vacum hose from your purge valve, this can be connected after the install of the manifold.
YOU CAN SEE HERE I USE THE FULL HOSE AND DID NOT CUT IT INTO SECTIONS
so once the new gaskets are fitted, install the maniflod and then connect the standard hose and fitting on to the back off the manifold, you will need small hands, but its not to bad, then once this is completed connect the purge valve hose to the extension you fitted and thats all the pipe work taken care off
Right if you don't have a m50 throttle body and want to use the 328 one, then you will need to use both gaskets, as the m50 body does not have one and uses the manifold gasket for sealing, the m52 body does have a gasket, so make sure you use both and also some gasket seal, there's a small lip the runs around the gasket where you can install the sealant, once this is complete install the body and job done and last but not lease install you new ICV hose to you boot maf and all is completed.
Please feel free to pm me if you have any questions, i have done my best to explain, and all this was completed for around £140 which includes the manifold, enjoy the power
ps i will edit as if i see any further advise i feel you may require
good luck and hope this helps