The safest and most conservative route to get the proper parts is through US Tower.
The best advice I can give you (and anyone wanting to build a tower) is to seek out the internet's Holy Grail of tower information: the TowerTalk email list on contesting dot com.
I'd bet your tower has already been discussed. The archives are on line with a search engine, and are an absolute *gold mine* of information for those who spend a little time digging.
and start with the searchable archives.
From this page you can also join the list.