Engines From the e32/e34
Generally seen as the best option for a 335i, this engine fits well in the e30 chassis because of the lower profile oil pan.  However, the motor mount brackets are more complex... Engine Position II and III are realized here, without modifications to the engine.

Engines From the e23/e24/e28
The oil pan from these engines isn't very well suited for a 335i.  If it were to be left unmodified the engine would sit too high in the engine compartment and the hood would not close (under normal mounting conditions).  It cannot be lowered because the oil pan would hit the steering rack.  Generally there are three possibilities:

1. Install an e32/e34 Oil Pan:
As stated above the oil pan of these engines has the correct profile to facilitate the 335i conversion, so it only stands to reason that the pan of the donor engine simply be swapped in favor of the newer model pan.  The use of this different oil pan does, however require that the oil pump from the newer engine also be substituted for the original pump.

Further Information on the Oil Pan Swap

e34 Oil Pan in an e30
 

e32/e34 Oil Pan BMW Part Number: 11 13 1 708 345

2. Install an Alpina Oil Pan:
Alpina used a custom oil pan for their B6 2.8/1 and B6 3.5. The use of these pans ended in 9/87.  This means that the Alpina pans are only suitable for Engine Position I.
 

Alpina Oil Pan until 9/87 Alpina Part Number: 11 13 115 or 11 13 119

(After 9/87 Alpina started using the e34/e32 oil pan.)

3. Leave the Existing Oil Pan Installed:
This is the least desirable of the three options.  This is only a valid option if the engine is placed in an extreme rearward position.  This option can only be used if there is enough clearance over the steering rack without changing the oil pan.  It is, however the cheapest of the three options

Questions, Comments?