The 5x4.5 kit widens the front track 0.75" each side, 1.5" total.
There are no reliable 3/4" hub centric spacers that I am aware of. However, spacers for the rear axle aren't necessary for any reason other than the aesthetics of equal front and rear track widths. There are reasons why a slightly wider track in front hurts nothing, and may actually be an advantage, but proper automotive engineering analysis is above my pay grade so I will leave that to the experts.
I did not use wheel adapters or spacers when i had the Yukon 5x5.5 kit installed. My rear axle shafts were dual drilled for 5x4.5 and 5x5.5 lug patterns so all I had to do was relocate the studs into the correct holes. I then purchased new wheels with the 5x5.5 lug pattern and 4" backspacing.
I am not aware of any spacers or adapters that would allow you to use TJ 5x4.5 wheels with the Yukon 5x5.5 kit which requires CJ style wheels with a 108mm (4.25") center bore. TJ 5x4.5 wheels have a 71.5mm center bore. No way that little hole is going to fit over that big hub.
Whose rear shafts did you use and is 108mm the actual OD of the hub?