I *think* (fairly sure) the 454 is externally balanced, unlike the earlier 396/402/427 engines, if so you will have to use a 454 balancer.

You might want to check with Jeg's or Summit to see if there is an aftermarket 454 damper in short version.

I have to think there is some way to make the long versions work, maybe you could move the radiator forward? Where is the p/s pump giving you clearance problems?