You were are all correct, it was an Allen wrench. I did as Wintersol suggested an got a 5mm Allen that attached to 3/8 drive wrench. Once they broke loose, I was home free. Hope I like the Mustang seat. I've been thinking more towards the Ultimate but this seat is in great shape and at half the cost so,
I had to try it.
Thanks for the help!
I put a Mustang seat on my VS800 Suzuki, and wouldn't go back to stock if you paid me!
My Valkyrie came with 3 seats: two-piece Honda, one-piece Honda, and a two-piece Corbin with back rest. I much prefer the Corbin seat; just fits me better, as does my Mustang.