my old 06 supra had a different tower design that folded inside the boat but was also called a Rad-a-Cage. it came factory with the stupidly heavy roswell 4 6.5" speaker sound bar. sounded like crap and was horribly heavy but state of the art for the time. it was also a head knocker as towers seemed to be lower back then.
this was my setup/tower but not my actual boat.

I upgraded to 6.5 hlcd's in the pod but if I could rewind the clock I would have followed mjh's advice with rev8's. I prefer the less harsh sound of the icon8's as hlcd's were not for me but rev's were all I recall back in the day. I don't think the icon's were around when i upgraded the tower sound. I'd mount on the back tab as mentioned. the other thing to keep in mind is whether or not you fold the tower so watch what they will hit. wiring for mine was ran down front tube so mounting speakers on the back tube would have left some exposed wiring from front to back tube but some good stainless wire sheath would hide it nicely.

good luck and post up what you do...