I checked the specs for Jag 3.8. It’s not really apples to apples with your setup. They’re twin 1.75’’ or triple 2’’. - HD6 & HD8.
There’s also two different jet sizes for the HIF6, 0.100’’ & 0.125’’. It’s important to know all this info before selecting a needle. Also, your carbs will have the spring loaded needles, the 3.8Jag’s have fixed needles (HD8 & 6) so I really need to know what you have first.
FWIW, the 3.8’s with triple carbs generally have the ‘UM’ needle (0.125’’ jet ) and twin carbs the ‘TM’ needle (0.100’’ jet).