So I am working on a design for a (you guessed it) 26" longjohn. I'm interested in using a top push rod, instead of the more common "below keel" method. But I'm not sure how to achieve this top push rod/heim joint method. Specifically the headset/steerer. With the push rod on top, I don't need to use a full headset (or do I?), I could just use the top half along with a length of steerer to accommodate the headset, stem, heim joint and any spacers I might need. But with that setup, there would be nothing to prevent the whole thing from separating from the bike if I pull up. What am I missing?

It seems like I have seen other cargo bikes with just the upper headset cup, but I've never examined a bike like that in person. stubby front loader | Flickr - Photo Sharing!

Bicycle Forge longjohn mk8.jpg