All vintage 289/302/351 engines had a 28 oz balance weight flywheel. The only time Ford changed that to my knowledge was the 5.0(302) HO around '81 or '82 was changed to a 50 oz balance flywheel.
157t and 164t flywheels both fit on the crank flange of any small block, which one you need will be determined by the trans bellhousing you have. Most 302 trans use the 157t flywheel but there are exceptions (like the AOD, which used a 164t flexplate on all it's engines). All 351 trans came from the factory with 164t flywheels. If you use the wrong flywheel for the trans bellhousing the starter will not properly engage the ring gear on the flywheel.
The front balancer needs to match the balance of the crank same as the flywheel. As far as balance goes, you can use a 289 balancer on a vintage 302 crank, but you also need to keep in mind which accessory pulley set up you'll be using. Older balancers used 3 bolt crank pullies. Starting in '69 Ford switched to 4 bolt crank pullies.
Since you're building a '71 engine, the balance will be the same as any other vintage small block so the simplest approach to get everything to fit together is to mimick the factory arrangement of the car you're putting it in. So, if for example you're building this for a '71 'stang you wouldn't want to use a 289 balancer because it requires a 3 bolt crank pulley and the '71 pulley is a 4 bolt variety. There's no reason you can't use an earlier pulley arrangement on the '71 motor, it just depends on what you have and what you're putting it in. It's just a lot simpler to get everything lined up and bolted together if you keep everything patterned after 1 specific application, because there were so many variations from one year to the next (like accessory brackets and pullies) that mixing parts from different models and years can end up causing problems with pulley misalignment.
