5 Speed swap

I still don’t see the issue. If a 904 with 4.10’s works behind a built engine with a bigger cam, then this will work also.

I'm not trying to disagree with you and am seriously considering swapping in the AX-15 I have sitting on my garage floor out of my old Jeep XJ, but... the key factor I think you're missing is the torque converter. Even a stock converter allows for 1000 RPM or more of slippage when the engine is at WOT during a gear change. So the actual RPM drop from a 904 with those gear ratios is quite a bit less than a manual transmission with those ratios.

@Kern Dog I fantasize about having a TKX in my Duster but $5,000+ on a kit from American Powertrain is just not feasible for me now. They apparently offer financing options now but idk how I feel about that, I'll have to look into it a little deeper. Do I continue running my 904 with 2800-stall TC and no overdrive and swap 3rd-members between a 3.55:1 and 2.94:1 depending on what I want to do with the car? Do I swap in an AX-15 manual with wide ratios intended for a truck or 4x4 that may break behind a 450HP 360? Do I take out a small loan to put a performance manual transmission into my classic car? It's a frustrating situation and you gotta compromise somewhere.