So I have a 1988 Subaru DL Wagon I got a few months back for $1400 with 60k miles runs great and It’s been my daily since February. But I’m wanting to upgrade the audio. I purchased the Metra 70-8900 harness adaptor, working on making a bracket to fit a new head unit but I realized with the set up I have I’m concerned that the alt and battery may need upgraded to compensate for the power I’m going to need for the amp. Has anyone done anything like this on their pre -90 Subie? I’m looking to install my 15s from my previous daily and the 1400w amp I have.