There were extra spaces on your script. It existed in at least 4 lines on your script. Find the lines below and remove highlighted:
Code:
if (KM1.checked && INCHES2.checked) {document.write(INPUT.value*39_370.0787)}
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.
.
if (KM1.checked && YARD2.checked) {document.write(INPUT.value*1_093.6133)}
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.
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if (MILES1.checked && CM2.checked) {document.write(INPUT.value*160_934.4)}
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if (MILES1.checked && INCHES2.checked) {document.write(INPUT.value*63_360)}
..the areas highlighted above which are underscores are actually spaces on your end. I did that in order to highlight the issue properly.
Hope that helps.