yep, that pic right there is the acrylic mod...nice example compulou.
Thats the easiest mod to do...Evan J. did it to his 75g as well horkn because he has that single central 250watt halide over it...he loves it. My only concern would be heat for some...the proximity can make things a little hot, esp over time when the sea-spray starts to crud things up.
So there is the option of using glass as well as a cross-brace...but yeah, if you are going that far, you might as well eliminate the need for a cross brace all together and euro-brace it.
nseawater, the plastic frame on a 65g is pretty much only to prevent the front and back panels from bowing. The cross brace is really the only critical support structure of the whole thing. Some may argue that it reinforces the corners because otherwise all that would hold the tank together would be silicone...but those people have obviously never made their own tank out of nothing but glass and silicone, or seen one made that way. So you dont need to add something to the sides at all. They are fine as is.
The sides need no support from the frame really...they are too short to bow. Its just the wide front and back panels that need the extra strength. I have made a couple tanks of thazt size w/o bracing at all, but we has to use 5/8" glasss for the front and back...lol. For the eurobrace mod, a strip along the front and back is all you need. Its length should be about 1/8-1/4" less than the place where it has to fit. If your front and back panels on a 65 are 36" long, and your side glass is 1/2" thick, then you would have 35" to play with, but better make it 34-7/8" to be sure. When in doubt, err on the smaller side. Technically, the eurobrace doesnt even need to be connected at the ends to the side panel...its simply a reinforcement for the front and back. Your tank right now might have a bead of silicone between the glass and trim...this might have to be removed ( razorblade time!)on the front and back to fit the glass snuggly into this corner where the glass meets the trim. Now worries though, when you silicone the new brace in this will all get sealed back up. When putting in the euro-brace, you silicone the corner that the strip of glass will be pressed into (the same place you might have just removed the old silicone, the corner that is 1/2 plastic trim, 1/2 glass), and then go back and add a filet of silicone, glass to glass, in the corner where they meet.
For the true 'euro' look, people then go and remove the plastic all together...but I wouldnt. The plastic trim is somewhat ugly compared to a true euro-braced tank, but it does protect the corners from chipping. It has a track for a glass lid, and besides...sometimes with those AGA tanks, the glass under the trim is some jagged-edged, beat-up looking stuff that you dont want to see anyways (hey, they built it to be covered up, so why would they bother grinding and polishing it, right?).