While there is ample information on the internet regarding the various GM 60-degree V6 variations, I will group them into two general families, rear wheel drive and front wheel drive (RWD & FWD, respectively). It is also fair to say that both families improved vastly since the original 2.8. See the links page for external sites devoted to the 60-degree V6 family of engines.
RWD engines have cast iron heads and the pulley arrangement extends farther out from the block. FWD engines have aluminum heads and more compact accessory drive setups, and they feature more modern internals.
FWD conversions are slightly more complicated in that the intake manifold needs to be reversed so that the throttle body faces the front. This leads to interference with the stock timing cover accessories. The solution is to use one of BCC's timing covers. We feel the many advantages of using FWD engines vastly outweigh the additional cost of conversion.
The MARC series of engine conversion timing covers are primarily designed for 3.1, 3.4 and 3.5 FWD engines, though they can be used on RWD engines with some component changes. Work is being done to also mate them to the new 3.9 liter GM engines.
All of the MARC engine conversion kits feature CNC-machined 6061 aluminum billet front covers, and come in three distinct styles.
MARC I and MARC III are essentially the same, save that the MARC I comes with integral outrigger-style engine mounts. The MARC III has no integral mounts, and requires external mounts. MARC I and MARC III covers give you the choice of either a Meziere electric water pump, or TCE's new CNC billet mechanical water pump. An electric pump frees up an extra 8-10 HP, while the mechanical pump allows the use of BCC's new power steering pump mounting kit.
The MARC II cover has the same integral motor mount as the MARC I, but employs a lower-cost, clockwise-rotating Fiero mechanical water pump.