If you plan on dual feeding you NEED the billet forward drum.
Scott McClay Transmissions, 200-4R Drum
TH200-4R Rebuild - Dynotech Performance - GM High-Tech Performance Magazine
Here are some links. I have a bunch more that include suppliers that have parts.
I started a project thing on this site and included some pix. I am moving along on my rebuild but my time is limited as is my %. Did you contact David Husek? He is a noted builder full of excellent info.