The L18T needle is almost the same as the A12GX needle. So no worries. But the dome spring is different that's an easy swap.

Hitachis don't have 500 needles. There are only about 20 for the 38mm carbs.

Hitachi needle comparo



See Hitachi Adjustment.

the linkage is easy ish, mine had a home made one of threaded rod cut to length, them 2 edges ground flat to fit into the carbs, then nuts holding and spacing some striker plates to the shaft. then a cable linkage to turn it all.

Just sold it to antoehr member, he might take a pic to give you an idea.

I didnt make the strikers, but had to remake the rod once.

Here is some of the info I came across:

http://www.jetlink.net/~okayfine/su/parts.html

http://www.jetlink.net/~okayfine/su/suneedles.html

http://www.jetlink.net/~okayfine/su/sumain.html

You don't need those needles. Just use the Hitachi needles.