I do like what you've posted and the links you've offered. I like the general design of the sewer-pipe drum dibbler, and the list of materials and the discussion.
There are quite a few hints. However, to actually build the drum dibbler from what's now given, I'd be doing a lot of guess work and trial-and-error. Of course I could do this, but I believe your intent is to make the process of DIY construction an easy one.
I believe a "next iteration" in the presentation would help alot. Suggestion: either do a well-illustrated (clear photos) MAKEzine-type DIY step-by-step article of the actual making and construction, or a well-shot, voice-over Youtube video covering that process.
Also, why not make the dibbler's handle/frame - which attaches at the hubs, an which you pull on to roll the dibbler - from something like 1" square steel tubing, welded? Wouldn't that be less flimsy and more durable than either plastic tubing or wood?