I've built many home brew hi steer setups. The only failure on any of my arms that I know of is Lilbuddy....but it kind of seems like he's been able to break just about anythink. LOL (sorry LB)
I used to heat the arms, bend them up and let them cool very slowly in a bucket of sand. Then I would dril out the hole to 3/4" and use 3/4" heim joints. You can use DOM for the draglink and tierod and weld in bungs to thread in the heims.
The more time you take on carefully heating the arms and giving them all the time they need to cool down before installing them the safer they'll turn out.
BUT, if you can at all afford it, buy some good built arms!!