Generally you can simply replace the needle with any other needle from other small block carbs. Simply thread in the new assembly from the donor. It may not have the same setting for the other engine as the old one did but it should work fine. I have swapped a .16 to a .18 and a .15 to a .12 in many cases just like yours. All of them work fine, the reasons I had to swap was I broke two, one on the .12 and the other was my .18. I had replaced the with the .16 and .15, and they were each made from different mfgs. So I will venture to say they are all interchangable. Just be sure to swap the whole needle assemblies and not just the needle, brass sleeve, fuel nipple, gaskets, etc. Good luck and let us know how it works out for you.