All the Wilwood calipers I've seen were 1/8" tapered threads. I just checked the Wilwood site and even their most expensive calipers are listed as 1/8-27 NPT.

Here's a link to a chart that shows how much thread engagement is considered correct. Remember, just as Denny indicated, the threads should reach the desired engagement when tight enough not to leak.

Also, be very careful with thread sealants, like Teflon tape. Be sure to keep it on the threads only. Don't let it roll over the end. It can tear off an get into your system. I like a Teflon based paste type sealant painted sparingly on the threads.