I think the Alfa trans is less than 75lb, but not sure by how much.... Seems easy to move around.
I also sometimes think that the Honda motors are overrated. Not that they are not great motors, but we put down alot of really good metal in the name of Honda sometimes. At least the Miata never cost more than $30k..., :)
I must agree with Eric. The 2.0 Twin Spark from the Alfa 75 (i.e. the name in Europe for the Milano) is a spectacular choice. I've just built one (OK, had it built by Autovolante in Miami) with trick-but-not-wild bits -- custom crank/rods/pistons/cams/valves on Stage II heads -- and it's been dynoed at 201hp and still nicely streetable. And it just drops in. (Autovolante's website has more details.)
Reinz head gaskets will make any engine reliability issue fade into the past.
There are tons of these engines sitting in boneyards in Italy. There are plenty of eBayers selling these. Or you can get one yourself for +/-$500.
The transmission, if you drill and back cut the gears, will shift smoothly and keep the synchros happy and healthy. I believe the weight of mine came in at around 69 lb.
Now, if you really want effortless "drop in" Alfa power, get yourself the engine from an Alfa 75 Turbo. The bone-stock engine with only a chip upgrade will produce 205HP @ 5500 rpm (up from 151) and 239 ft-lb of torque @3000 (up from +/- 170...oh, and it's spread nice and flat from 237 @ 2500 to 203 @ 5500). Now, if you want to go crazy with those custom bits...
This is my next project, incidentally.
-Joe in SoFla