I'm in the process of building a lower too. After doing some searching, I went over to Harbor Freight and picked up these to aid the assembly. I probably didn't need them, but since it's my first build I figured that I may as well make my job easier, and I can certainly use them for future maintenance or builds. Plus I got to buy myself some new tools.
http://www.harborfreight.com/soft-face-mallet-39528.html
http://www.harborfreight.com/spring-loaded-center-punch-621.html
http://www.harborfreight.com/5-piece-long-drive-pin-punch-set-93111.html
I also purchased a vice block from eBay for about $20. That definately wasn't needed, but it will make it easier.
http://www.harborfreight.com/soft-face-mallet-39528.html
http://www.harborfreight.com/spring-loaded-center-punch-621.html
http://www.harborfreight.com/5-piece-long-drive-pin-punch-set-93111.html
I also purchased a vice block from eBay for about $20. That definately wasn't needed, but it will make it easier.