Need help w/gear and slick size on a 402 Duster

I will assume you have a big bolt pattern axel, but my suggestion if it is a street/strip car would be to go with a 3.55 gear and a 26" tall tire, for your combo it would do really well with a 235/60/15 BFG drag radial and that ratio, should be able to dead hook on grease. I used to run 11.50's all day long with my 408 when it was in Demon with 26" BFG's and 3.91 gear, but I had a little more motor than you. My thought would be that the converter is probably a little tight for your motor to go 106 mph. A 3500 stall 10" would be a good fit IMO. Lots of Big Bolt pattern wheels available for different backspacing but IIRC a 15x8 wheel with 4.5 inches of backspacing will fit without having the leaf springs moved in.