Motor Mounts on a 66 with a 350

[msg]

The motor mounts on my 66 c10 with a 350, look like they need to be replaced. The driver side vibrates pretty bad, has the alternator bouncing around.

Ive never replaced a motor mount and could use some help.
The mounting brackets seem fine its just the rubber inserts that are all cracked up looking. What are the better mount replacements to look for?
Summit has these polyurethane mounts but I dont know if rubber might be better.

http://www.summitracing.com/parts/pt...l/media/images

Also how do I get the right part to fit what I have?
Looks like this..