Mechanic checked the temp and it read 185 on my 88 GTU, but my dummy guage reads above half to 3/4.

 

Where on the block (or t-stat housing) did the mechanic take the temp? If he used the original sensor spot, then you have a (slightly) out-of-cal gage, just keep this in mind as you're driving...On my S4, on hot days (like now), she'll run at 1/2, a little more when I'm romping on her, but never 3/4 (I'd start to freak at 3/4)...