My 87 has a box with both ports on it but the fresh air holes 
are blocked. I ended up using an early 87 box and swapped to the fresh air ports. I am thinking of swapping the pass side 
back to the metered air for my wife. She always has the fresh air turned off. I just don't know if it will throw the box's
air balance off somehow. 

Bill

On Aug 28, 2012, at 10:40 AM, mark drillock <mdrillock@COX.NET> wrote:

> The key is the large hose connections on both sides of the box. The
> original fresh only side air boxes have round connections for the large
> hose on each side and these connect very near the front of the van. The
> later boxes with side heat use oval connections for the large hose on
> each side and these connect to the box area farthest from the front of
> the van.
> 
> The original set of side connections is in front of the heater core,
> fresh only. The other set is behind the heater core, so when the core is
> warmed the side vent air is warmed.
> 
> Many later boxes have both position connections available but the pair
> not used are sealed up. To switch from one connection point to the other
> means different hoses, at least in the case of wanting to use the oval
> heated air ports. These heated ports are in tight areas of the dash that
> require special molded elbows to adapt from the oval box ports to the
> round vent hoses.
> 
> The switch from fresh only to heated side vents occurred during the 1987
> production year. Early 87 uses the old hose connection points while
> later 87 made the switch.
> 
> Mark
> 
> Frank Condelli wrote:
>>         Does anyone know how to tell the difference between the front heater boxes that have heat output to the side vents in the dash and the ones that do not ?  What can I see from the outside of the box that would tell the difference ?
>> 
>> 
>> 
>> 
>> Cheers,
>>