Choosing a converter has me pulling my hairs.

Depending on your main purpose for the car 3:55 gears might do you fine. That's what I have in my Cuda now with 28" tires so it's a very mild cruiser down the hwy but yet it still runs decent. Of course it's not as quick as the 4:10's it had but we like to go to alot of cruise-ins and some are as far as 50 miles away so the 3:55's are naturally much better for those drives. I ran 12.91 with the 4:10's and it ran 13.56 with the 3:55's and that was on a bad tune. Since then I got it running much stronger and think it'd be in the 13.30 range. This with a mild 360.

I think your right that 904's start at 10" converters with PTC.