In reply, I don't think the 2.5 runners will seal on the 2.7L heads. I've got all the parts (2.7L head and both types of intake runner) and I can get a look at the exact measurements tonight.
With mine, I was going the other way and put a 2.7L intake on a 2.5L engine. That had plenty of surface for mating the seal. The gasket of the 2.5L runner looks like it will fall inside the 2.7L intake though:
I see two fairly simple ways to modify.
- Make a rigid plastic or metal adapter plate to fit the 2.5L intake passages and give them a surface to seal onto.
- Use the 2.5L cable throttle on the 2.7L intake. 'Adapt as needed' to fit. Block off the resonance cross-tube. Mid range airflow will not be optimal, but it's a compromise already, running on the 5.4 DME (ECU).
Here's an ugly adaptation making a 2.7L throttle work on a 2.5L engine. Tubing clamped onto tubing to make it fit. Not my work or preference, but it did run pretty well. You would want to go the other way 2.5L throttle onto 2.7L intake.
Much more complicated and has a few details I'm sure I haven't considered:
Run the 2.7L engine how it was made to be run. Swap in the DME/immobilizer box/key fob, gas pedal, and adapted wire harness from the parts car. Keep the 2.7L engine intact as stock.