I've been looking at some cams that thump too. I'm trying to get the smallest cam I can that you can still hear it. I have a 350, but the 305 won't be too far off.
For my truck with a 350 I've about got it narrowed down to a comp cams xe262 or xe268. Here's the specs from Comp:
XE262:
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=85&sb=2XE268:
http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=86&sb=2Here's a video of the xe262 in a 350. being in a 350 means it would be a bit lumpier in your 305. I'm pretty sure in a 305 I'd get the xe262.
http://www.streetfire.net/video/83-Z28-Cam-idle_99231.htmHere's a xe268 in a 350, again it would be a little bit rougher in yours.
http://www.youtube.com/watch?v=kukI2LnxrqY&feature=channel_pageI've been looking at the thumpr, and I'm just not sure enough how it would be in a big truck. it makes good power but it makes it way on up the rpm range.
Here's a thumpr vid for fun it's in a 350.
http://www.youtube.com/watch?v=j97kabzMOYA&feature=relatedAll the cars in the videos are idling in park or neutral. if you have an automatic, when you put it in gear, it will lope even more.
Like capt said, all of these cams require new springs because of the higher lift. along with the lifters, etc...