Tire question

Sportster 48...going for more of a vintage look and changing out the tires. The rear i plan to go with a 500-16 which matches the stock size of the tire currently on there. For the front is where i have a dilemma. Do i go with the same size tire, 500-16, which i know will fit or would a 400-18 work? The required rim size is 2.5" but in the specs it says alt sizes would be between 2.15 - 3.00" which looks like my rim would be at the max size on that chart.

Could i encounter any issues with having a 400-18 on the front? Width wise i would be 20mm thinner but overall diameter but overall diameter the 18" would only be 8mm taller.