Don't knock a guy because he's 19 years old....
His post may have come off as a bit "know it all" but he very well may have installed 100 shift kits. I had probably done 50 by that age....and rebuilt a handful of Th350 and 400's.
I was certified as an ASE Master Auto Tech by the age of 20 and at that time had been in the military as an infantryman for over 2 years.. So I had quite a bit of experience before I was even 18.
As Crosley stated, a torque wrench isn't a MUST on a Th350 with a cast iron VB
The TransGo kit is better quality and it does differ.
My recommendation on the B&M is to leave the 2nd checkball in place and maybe go a bit less aggressive on the 1-2 feed hole. Other than that it can be made to work.
On a Th400, the TransGo Reprogramming kit is the only kit that dual feeds the direct clutches without internal mods....
Well worth the additional cost.