Being a proponent of using as heavy a bow as one can handle well, I've been following this post since it started, just not chimed in till now.
TurkeyFoot, glad you found one, and that is a really nice looking bow for sure.
I've been using my 75# Blackwidow T/D longbow for quite some years now, on everything from Bunnies to Buffalo (our Water Buffalo), and based on my limited Buffalo experience, with 1000+ grains, perfect arrow flight and a properly sharp 2 blade broadhead in the right place from that poundage bow, I reckon you should be golden.
Please do share your journey on getting it tuned, and definately share your hunt.
Looking forward to the next chapter of this.
Best
Lex