1. you probably shouldnt "get down" on something untuned (especially since you changed motors)
2. Tach signal, and distributor correlate, if your dizzy is acting funny it will make it jump around, make it feel like it has no power, break up, etc etc..
3. what plugs are in the motor? Hopefully Bkr7e's gapped accordingly.
4. Dont blame a tune on a motor that doesnt seem to be running properly period.