I had the same problem, figuring on the fact that alumacraft didn’t change front pedestals mounts you have a:
9″ round base springfield plug-in pedestal (but no 3/4″ pin hole in the middle (solid))
I wound up replacing with a:
9″ round Springfield Taper-Lock base $17
Added a:
Springfield Taper-Lock™ Adapter $17
And I now have a 3/4″ pin base that is rock solid, and the holes line up perfectly (no re-drilling or worrying about what carpet is underneath the original base).
I installed this versus just a Springfield Pro Seat as I like to use a Swivl-Eze® Offset Pin Post as I sit alot when using the trolling motor. I have noticed Alumacraft’s are not designed it seems for the foot type control trolling motors (power drive is fine) as there seems to be little room for the foot control and cable when sitting down in a seat.
The Springfield Pro Seat is the one that accepts any 3/4″ pin butt seat (the most common). There is also this one: Control Post Seat which is a little more pricey but has the same pedestal.
Hope this gives you a few options.
NOTE – all images stolen from cabelas and bps. I don’t think they mind considering how much I spend in a year with them!