Ceiling pot light conundrum

Installing %&^% ceiling pot lights at the gf's house. Because she has a bungalow, the lights have to be conatined within a metal box with the vapour barrier, etc. to hold back insulation in the attic The lights have 'ears' that are supposed to open on the other side of the metal box rim once the lights are mounted. Essentially it 'sandwiches' the ceiling drywall between the light rim below and the metal box above it.
Problem is it is an older home and the ceiling has 3 layers of drywall, one of them plaseter and lathe so the depth is too wide for the ears to go into the box as intended. If I dug out a notch they would probably fit into the drywall on either side, but I do not regard that as a particularly robust attachment scheme.
To me it just seems easiest to basically use self tapping screws on the inside of the light that just go in above the lip of the metal box. If I put 4 roughly 90 degrees apart around the light I would think it should do the job ok. Other options that I can think of are a labour of love which I am not prepared to undertake.
Before I do this, I thought I would check here in case there are any other methods, special part #XYZ MKII from Taiwan, or tricks that someone here may have already discovered or invented for a case like this.
TIA bigtime!.
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I understand what you are thinking about doing. I can't say for sure how long that method would keep the cans up tight against the ceiling. What I try to do in situations like this is make my holes adjacent to the joists. Then I drill a few holes in the side of the cans and screw them to the joists.
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There's a new product, due out this month, that might make all of your carpentry problems disappear. See: http://www.lightingfortomorrow.com/2007/yearbook_honorable_in_maxlite.shtml I didn't see the "Faux Can" listed yet on the MaxLite site; but it might be worth a call.
TKM
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