Ahh you want to use an interheater. Remember heat rises. Those units are proven to NOT work in a Subarooo, I doubt they will work for your app that will have more than twice the intake airflow.
I would recommend scrounging up some other core. If you are fixed on a top mounted installation then look at the earlier RX7 unit.
The only reason a manufacturer ever used a top mount unit is for assembly line ease. Drivelines get installed complete from under the vehicle and the manufacturers needed a device called an intercooler for marketing purposes. So instead of installing an intercooler that actually works they just stick one on top of the engine where it can be shown off with the hood open, cool. Why bother.