《现代汉语方言音库 • 成都话音档》has two listings for 虾 one that says:
xa⁵⁵ can pretty much be pinyinized as
ha1 - for simplification here.
And there is of course a second entry that says:
Now of course it looks like I've answered my own question - seeing as the name of the book is 成都话音档. But,
ha1 is not a pronunciation I've heard before for 虾 in Sichuanese and most people don't believe that it even exists. I'm curious as to where this pronunciation is still maintained in Sichuan.
It's certainly part of the vestiges of 湖广填川.