It does not have the tripod ring, no.

 

Is it heavy enough to need it?

 

no, it's not really that heavy. BUT at 300mm (and definitely at 420 w/1.4TC) you'll want something stable to rest on and/or a high shutter speed. TBH, it would be even better with the ring, but I haven't found one used. New they're $120. I haven't looked that hard, though.

 

I would like to use this lense for surfing shots. How well do you think it would preform. Could i use a tube extender on it or would this diminish the quaility?

 

It is perfect for shooting surfing

I don't know where you're located, but it will be excellent for any break down the East Coast. It may be a little short for outer-reef breaks in Hawaii. I doubt you'll need a teleconverter (extender), but they are nice to have regardless.

In shooting surfing conditions f4.0 is plenty fast too

 

thanks for the tip, pointy