Tom,
I wouldn't even bother trial fitting the motor- it will fit perfectly- almost like it was made for it.
My ERA is the only thing I have ever worked on where everything lined up and bolted together exactly as it was supposed to. Just look at the links that Jim posted and Bob P's diagrams, bolt on the mounts and drop the motor in. The modification to the motor mount that John 550 suggested (and which Jim posted the link for) is a good idea b/c you will get some motor torque.
Good luck.