I canít help you with regards to your tubes, but can offer my humble opinion on steering, There are many choices for aftermarket, high performance set-ups, youíve named two, I would add to that ĎLathamí who make excellent, if rather expensive kits.
I think without exception, they all mount Ďfore & aftí from an extension of the tilt tube, to a wing plate mounted at the rear of upper mid section. This configuration is emmensly strong, and if fitted/piped properly, would be virtually unbreakable!
Another nice option on the more performance orientated steering systems, is the Capalino helm unit, whilst not power assisted as with sterndrive applications, you can adjust the displacement of this pump, thus changing the hydraulic ratio, and therefore the number of turns lock to lock.
I have an IMCO dual ram set-up on my twin bravo installation, this is of course power assisted, but the principle is just the same, the Quality and reliability are superb.
Hope this helps.