All 302's 68-81 is 28oz imbalance and 82-95 are 50oz. If you are running a 5.0L 82 roller motor then it will be 50 oz. Balancer and flexplate.
There is no factory 50 oz. flexplate with 157 teeth that is made for the C4 trans. They are all aftermarket pieces since the small bellhousing, case fill, C4 wasn't used behind any 50 oz balanced 302s. The dimension of my F/P counterweight for 50 oz. is 4 1/4"x7/8"x7/16" thick. The classic Mustang should use a flexplate with a 157 Tooth Ring Gear and the diameter is 13 1/4" with a 10 1/2" bolt circle for the torque converter. I sourced my F/P from Ford Racing Performance Parts. Other vendors have them also. The FRPP P/N M-6375-E302.
The factory 50 oz. balancer should have the P/N E4TZ-6316-A. It will use a 4 bolt crank pulley. The timing marks on the balancer will need to be repositioned for use with early timing covers that have pointers which are at the 2 o'clock position.
The cast in counterweight on the 50 oz. balancer should, obviously, be larger than the 28 oz. when a side by side comparison is made. The aftermarket is now making 50 oz. balancers for use with the pre-1970 3 bolt crank pulleys, if desired. NPD is one source. I think that the timing marks on them are for use with the early timing cover, also.
I just noticed that this post was initiated in 2005. Talk about digging up the past. :scratchchin