4-speed to an Auto Swap

OK, I know it may be sacrilege, but I’m seriously considering swapping out my 4-speed for a TH400 auto. I have most everything I would need; a TH400 out of a 68 442, a decent console, excellent shifter, auto pedal assembly, linkage, etc. I know there is a kit to convert the 2-speed shifter plate to a 3-speed plate. The only thing that I think may be a concern would be the flexplate for the torque converter. Does anybody know if a flexplate for a Jetaway would work for a TH400, and would it be strong enough? Or is there a heavy duty flexplate that would bolt to the early crank bolt pattern?

Just knocking it around right now, but I am seriously considering this swap.