The kits from that site say that you need a 10inch or smaller converter.
Isnt the stock converter 12inch?

 

i had a b&m and i loved it, you should deff get one

 

It's not that you "need" it, he's just a firm believer that running a smaller higher stall converter provides the "cushion" to the trans that helps prevent parts breakage under hard use. If you're running stockish type power, there's no problem sticking with a 12" converter; just let him know and he'll give you the info to set up the HD2 kit accordingly.
I've run the kit with the stock converter in my truck, and you need to go with zero washers in the 1-2 accumulator and stay at the minimum recommended "2nd gear apply" hole size in the separator plate.
Always use the 093 (Vette) servo. I tried it one time without it, and it's impossible to get a good-quality 2-3 shift.