First, you will not be able to use the existing hardtop or pipework, it was not ment to support that weight, nor is angled correctly or ever intended for this use. As far as adding a tower, it can be done, but honestly it will make that boat rock a lot more. A 27ft boat with a tower is pushing it, the only boats that can pull it off are inboards or I/O's with jack shafts where the engines are located close to the center of gravity, here, adding a tower will have less effect on changing that since the bulk of the weight is located here already. You will see a drop in speed and economy as well. Honestly, no walkaround has the room for tower that will be very functional. I'd also be concerened with where you would mount the tower, I have a feeling structurally you might need to beef up those areas, or atleast make sure they are located over structural bulkheads, not just any bulkheads. Honestly, I'd buy a bigger boat or different boat if a tower is a must, or try to live without one. About the only 28ft boats that do OK with tower's are Carolina Classic's, albemarle's, and Henriques's, but they are much heavier and none have outboards. I've been on a few under 30 ft walkarounds with tower's, and just about ever one rode horribly.