You said 320/6 right? Very similar to the 323i, the top two engine to transmission bolts are real buggers to get too, I had to use 3 one foot extensions with wobblies to reach them, if you remove the radiator and tilt the engine back (being very careful not to crush the heater core hose at the back of the cylinder head) they are just accessible by going over the transmission and having someone with little fingers guide the socket onto the bolts. The only other hurdle is the starter bolts, one is easy, that's the one you can see, the other requires a special tool because it's behind the starter motor and under the intake manifold, the special tool is this crescent shaped wrench that also has a spiral to it that allows you to hold the nut as you loosen the bolt from (yes you guessed right) the back of the transmission.
Hopefully this is enough information, I wouldn't say it's hard if you know the procedure, but it is time consuming and can be frustrating.
If the body of the car is sound I'd say do it, the m20 engine was very reliable, if your 525i is 91 or earlier it is essentially the same motor.