235 60 16 are the same height at 255 45 18 so it will sit the same.
the ride will be a little stiffer in front becasue lowered a arms are not made to be used with lowering springs. i just had to drop it becasue it was to high for me stock.
rear i did not have to notch at all you do have to cut off the top of the bumpstop though. what id do is get 3 inch drop sprigns (i did a blazer x yesterday it dropped it 1 1/4 more inches than the stock springs so the springs arent a 2.5 drop) and 3 inch block in back and wait for spindles to come out and when they do put spindles in so its slammed. but belltech has been lagging on the spindles for the last 8-9 months