Hi,
A few photos in my how to thread below.
https://www.volvoforums.org.uk/showthread.php?t=263081
The drivers seat has height adjustment and a flip down arm rest neither of which are on the passenger seat.
156 is a 4 door so the front seats don’t flip forwards- Alfa 147 seats look very similar and do flip forwards as the 147 is a 3 door. I had a set of 147 seats first, but despite the seats looking similar the bases are quite different- after a while making brackets etc I admitted defeat, sold them on and bought a set of 156 seats.
Hope that helps,
Cheers