can i take a 91-93 grille and pute it on a 84 with little or no mods?

Yes, you can switch the two grilles. However, the headlights are mounted about 1/4" to 1/2" higher on your 84 then on the 91-93. Your headlights will not have even space around the headlight opening on the 91-93 grille. But, if you don't mind that it will work.
I have just switched the grille on my 84 to a 91 and didn't like the space so I replaced the rad support. I emailed a template I got off the web to you which will relocate the mounting points of the headlights

Have fun !!!!

ok i sent you an email
thanks