Need info on electric fan for 76 GMC

I've got a 76 GMC Sierra that i've been working on for a few years. I got the motor rebuilt, which is a 9.0:1 .030 350sbc, which should be around 350hp. The fan i've got on it now is one of those stock clutch fans which is getting loose, and think'in about some sort of electric fan, to slap behind the 19"x31" Griffin aluminum rad. Im not shore how big the fan needs to be, so please advise