360 magnum into '66 Valiant

You might have to cut and reform the transmission tunnel to fit a 727. If so, why not use the transmission which came with the 5.9L Magnum, as many have done? That gives overdrive and a lockup torque converter for better mileage. I have a 727 short-block transmission w/ cable-shift for my 1965 Dart 273. Never installed and might never. I understand one just needs to beat over the pinch-weld to clear the trans tunnel. Downside is more parasitic drag than with the 904 currently in it. I think the 727 came in trucks. Might be better for drag-racers, but I'll never be doing that. Anyway, perhaps a lever-shift 727 SB will fit your 1966 if you take a hammer to that pinch-weld which drops down in the tunnel.