Windshield Washing Fluid Reservoir
Since the air box of the M30 will be located where the e30's windshield washer fluid reservoir was, it needs to be moved.  A very elegant solution to this problem is to use the washer tank of the 324td.  This tank is to be located where the battery would go, were it under the hood.  The 324td never made it to the US, so such a piece will have to be imported.
 

324td Windshield Washer Fluid Reservoir: BMW Part Number 61 66 1 385 280

In their H35, Hartge shifted the reservoir to the trunk.  This can be reproduced, but may cause flow problems if the car is to be driven in cold climates.

Shifting the Battery into the Trunk  
Shifting the battery of the cabrio, touring or 316i-320i to the trunk is very simple.  All the parts can be taken from a 325/i/is/ix/e/es or, of course purchased new.  The installation will require holes to be put in the firewall, along with the installation of a positive terminal under the hood. The cable will be a little short with the cabrio, but it can be done. 

Proper precautions must be taken to insure the battery and all terminals are protected from contacting the metal of any body work.  The cables under the hood must also be properly reinforced to prevent them from contacting each other, or bending.  An appropriate cable must be used here.  The factory cable of the aforementioned cars is highly recommended.

Coolant Overflow Tank
In the older model e30's the coolant overflow tank is located on the passenger's side.  This will be in the way in the 335i, and it and its mounting points must be removed to accommodate the air box of the M30.  The tank is to be relocated to the driver's side.  The parts from the newer (7/87) e30 can be used to accomplish this, as the tank was on the driver's side in these later years.  This is also a very aesthetically pleasing application.
 

e30 Overflow Tank Beginning 7/87: BMW Part Number: 17 11 1 712 641

Air Cleaner Box
The air box of the e32/e34 is very well suited for the 335i conversion. This modification also improves the aesthetics of the engine compartment.  It also has an improved volume and flow rate, as compare to the metal air boxes.  New, this part will cost around $161, so it may be advantageous to check the scrap yards for it.  If the car is not to pass any inspections, a cone-type filter such as the kits made by K&N can also be used.
 

e32/e34 Air Cleaner Box: BMW Part Number: 13 71 1 707 727 Bellows (to AFM): BMW Part Number: 13 71 1 707 767

Questions, Comments?