Another Mopar Off My Bucket List - Barracuda Fastback

I believe the only option you have that is anywhere near efficient is to add the 4" inter cooler to the top of the manifold. You can try to get something into the manifold but it won't be big enough not to heat sink and be useless.
I have had this conversation more than once with a very good FI builder. He builds high buck TT setups on very spendy cars for a living. The heat soak is worse on a blower car because it is working ALL the time.
One thing to check though, is that if whatever core you use, be sure it can take the pressures of an A/C system. Most of them aren't made for higher pressure systems.