67 Barracuda Heavy Electric Load

Okay, it been a while but still chasing this issue. Dallas Auto Electric says I need a different type of alternator that puts out more at lower RPMs. According this the shop, the alternator I took to them is a high output alternator but only at higher RPMs.

So the recommendation from them is that they build a new alternator for $300 but I need to get a new / custom mounting bracket. They are going to get me details on the bracket. I also asked if the new proposed alternator would put out too much at high RPMs and they said no.

Does this sound like a reasonable/plausible solution?