its good to replace the lifters, since most people doing cam installs are doing them to untouched stock shortblocks.

if you have a stock setup...and you dont mill the head, you should be just fine with 7.2" OEM pushrod lengths but its always good to check before you go ahead and do it. the tool is like 20 bucks i think. if you go with a higher lift cam, get springs. personally if your on a budget, spend like 500 bucks and get the LT4 hot cam kit, it comes with everything to convert it over i believe, and it is decent gains.