I am considering using a 350 water pump and timing cover on a 455 and wonder if this will cool the 455 sufficiently.The 455 water pump is from a 73 and seems much larger as far as the divider plate goes.I want to use the complete accessory drive which came on the 350 and I understand they are all the same for 1968 V-8's.If this has been done successfully by anyone I would like your input.  

As far as I know, 350/400/455 water pumps are all the same for the same YEAR.  There was a design change about 1968 or 1969 IIRC.  I'd use the 1973 one, even in a 1968 chassis.

Much more important to cooling is the radiator because the thermostat controls the flow, not the water pump per se.  Get a new "Desert Cooler"-type for A/C radiator and you'll be "cool".;-)  

Don't forget to install the internal baffle plate and the transfer tubes between pump and cover.

Do use a new thermostat (170, 180 or 195--I prefer the latter).

If an AT, then use an external cooler mounted in front of the radiator--do not use the internal cooler in the rad.

Don't forget the shroud.  Also, use the factory viscous-drive fan, not one of those cheap aftermarket (and noisy) fans.

I live in Southern Nevada where it can get near 120F in the summertime.  Follow the above and you won't have a problem.  

I have the desert cooler radiator with a 180 Tstat.I guess what I am trying to do is make the 455 look like a 400 by using the 400 style accessory drive and bolting it up to the 455.Since 455 engine were not available in 1968 you want it to look the part.Plus all the pulleys on the 455 were junk.So Barneyformula said use the timing cover and dampener from the 68 motor I have and it would let me use the good 68 pulleys I have.I live in the socialist state of MA. so the summers are not quite as bad as yours.This being said the 455 water pump looks better as far as capacity and I wanted to know has anyone successfully used a 68 older style waterpump on a 455?  

I guess I overanswered your question. Short version: yes.