Like Sniper03, I use the clevis pin trick and it really helps. Get the 1/4" size, as I remember it was about $1.50 at Lowes. I had to file it slightly as the hole was rough and I didn't want to force it through the lower. Just a little touchup and it inserted nicely.
Car54's dowel looks good too.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek