LD 340 vs Performer RPM?

TonyFields,

Does the air-gap runners and carb deck sit higher than the LD340 in order to get the gap or does it have a "valley pan" cast into the bottom to achieve the gap?

I was wondering if one made a valley pan for an LA motor would that give a similar affect of keeping the carb and runners cooler (block the heat risers of course)?
The valley pan is lower on the air gap. runners and carb deck are the same as the performer RPM and realy close to same as the LD340.