Keep the stuffer and 38 Mik. Carb. You need to find out what curve is in you motoplat before we can decide where to set it. The way you set it is with a dial indicator and so many thousandths or millimeters before Tdc. Unless you fly wheel is keyed and the plate has slotted holes not usually the way they are.

Where do you think its lean? Will it hold a steady rpm at specific throttle settings. 1/8, 1/4 ,1/2, 5/8 ,3/4 ?
Is the motoplat tested good for sure?