About mixing layout, it seems to work, but to work properly it needs that all the layout positive position to the elemens ( x@y with x and y positive ).

There is also a problem with force based layout, because nodes are displaced every time and not only at the very end.

There are still lot of improvements that can be done, but you can try.

MCHttpRepository
   location: 'http://smalltalkhub.com/mc/MathieuDehouck/RoassalAlgorithm/main'
   user: ''
   password: ''

package: RoassalAlgorithm

Regards

Mathieu