Depends on what year 325i, If it's a E30 325i then yes the heads will bolt up on the eta 2.7 M20 engine. However your going to drop the compression ratio on your eta M20 because the i M20 2.5 had different taller pistons then the eta M20 2.7. If you plan on boosting it's a good idea if not your going to lose power from doing the swap. You can however swap the camshafts and valve spring over to the 2.7 eta M20 from the i 2.5 M20 and gain some significant top end power. The i 2.5 M20 has a more aggressive cam grind and stronger valve springs then the eta 2.7 M20. If you want the most bang for your buck I would run the Eta 2.7 M20 motor with the I 2.5 cam and valve springs with a Dinan performance chip or the 325i ecu.
This swap is in the cards for me in the spring, I've already installed the Dinan chip and seen a considerable increase in power.
1986 BMW 325e
1990 Mazda Miata MX-5
1981 Honda C70 Passport
Anything with an internal combustion engine.