Maybe there where other issues with your build, I have put more ls/vtecs together than I can remember...

http://www.modified.com/tech/0411scc...ine/index.html

Here are the lengths of each

OEM B16A : 6.85"
ARP B16A : 7.125"

OEM B18C1 : 6.75"
ARP B18C1: 7.250"

so either way you go you should be fine...