I have a 30' Scarab with Stellings EB and the prop shaft is .75" below the bottom. The boat planes fine with Bravo 1's. My thought for a heavier 38' boat would be to set up with the prop shaft at 2" below the bottom with the drive shaft angled down at 2 degrees. This will allow you to drop the boxes (if necessary) 1+" and now the drive shaft would be still at about a 2-3 degrees but at an upward angle. One of the primary reasons the box project is expensive is due to the extensive re-rigging required to do it correctly ( new engine mounting, exhaust mods, plumbing, etc.) This is not a bolt on project.
Sprague

Study the designs of both Stellings & IMCO boxes. When considering boxes take into consideration the IMCO uses a much longer than stock drive shaft and the Bravo coupler. The Stellings uses a a direct (double u-joint) bolt on connection to the carrier bearing in the box.... no coupler or unsupported shaft. A whole lot less damage to be done if (God forbid) if a u-jount breaks in a Stellings rig, it will not destroy the bellhousing.
Also, you can pull an engine without removing the drive with a Stellings.... you cannot with an IMCO.

You can also use my On-Board-Dyno on the stellings box!

I am also considering an ext box,
does a( neutral) box help or hinder bow lift,.,. wil it help a hull that needs bow lift or hurt it?