RigChange

I have a 1993 Legacy my motor ran great but it would over heat. which I was told that the heads needed rebuilt. but it also had 336000 miles. I found a 1.8 on craiglist.org. the man told me it had only 75000 miles on it. so I pulled the 2.2 out and replaced it with the 1.8! It starts and operates with lots of power. but the lifters, are tapping very loud. So the man said this 1.8 engine came out of a 1993 Impreza. I am thinking this engine has hydraulic lifters that supposed to adjust themselves. "Question is: should I rebuild the heads or is there something like a sensor or the fuel injectors causing the tapping noise? My 2.2 injectors work well but when I used the 1.8 one set of the injectors were not working so I have one set of each until I get the new ones.