Need help with converter

A few things to keep in mind.
Flash stall and brake stall rpms will vary with the engine's torque. Just because PTC calls it a 3500 rpm converter, may or may not mean that's what it will actually flash to behind this engine. If its what they call this particular converter, then it won't. It takes a certain amount of torque to attain a given stall number.

Drilling flexplates. Me - I wouldn't do it. I've broken too many flexplates. If you have a self centering bit, feed it so the heat buildup is minimum and its probably OK.

I'd take a look at the Mopar Performance Chassis Book to see what guidance they may provide. Also see what info you can get from Turbo-Action and maybe a third manufacturer as well.