PlanB wrote: Thanks Dave. I read that long thread a while back about using the back end of a gearbox & all that rigmarole with oil seals. I never did figure it out. Why wouldn't you just fit a universal joint to the motor shaft, hook the tail shaft onto that & be done with the gearbox altogether?
You really need to look under an MX-5. Although I'd be surprised if there aren't enough photos of the underside of an MX-5, between us and Ian Hooper and all other "Miata" conversions on EV Album, to enable you to grok the whole PPF (power plant frame) thing. Here's one of Ian's, with his motor and adapter in place of the gearbox
The PPF is a truss beam that connects the gearbox casing to the diff casing, running alongside the propshaft. The gearbox does not mount to the chassis anywhere. Its casing forms a structural component between the engine and the PPF. The whole drive-train, consisting of the engine, gearbox, PPF and diff, bolts together into a rigid assembly that is hung from 4 points -- the two engine mounts and the two mounts on the "wings" attached to the diff.
When eliminating the gearbox, the motor will need two beams that go forward from its feet to the original engine mounts, and it will need to somehow connect rigidly from its flange back to the PPF.
That's the motor
casing. Now consider the shaft.
The distance between the motor and the diff will vary plus and minus a few millimetres as the car goes over bumps etc. and the chassis flexes. That's why the propshaft always has a spline somewhere that gives a sliding joint. As with many vehicles, the MX-5 has a male spline on the gearbox output shaft and matching female inside the propshaft. It also has a bush inside the tail end of the gearbox casing, that forms a plain bearing with the outside of the propshaft that supports it and stops it flopping about on the spline, while still allowing it to slide in and out of the gearbox by those few millimetres.
You can't attach the propshaft or its uni-joint rigidly to the motor shaft or there will be extreme end-thrust loads onto the motor bearings and diff bearing (unless you add a sliding joint somewhere else in the propshaft).
You could design and manufacture an adapter to go between the motor and the PPF, containing a bush or bearing to support the propshaft, as Ian Hooper does here (also having to lengthen the propshaft):
http://zeva.com.au/conversion_blog.php?post=12
Or, as Ross Pink did on his eVan, and I suggest on the MX-5, you could make life simpler and unbolt the tail section from the gearbox and use a simple adapter plate between it and the motor flange. And rigidly couple the sawnoff gearbox output shaft to the motor shaft (as it appears Ian might have done).
Don't worry about the oil-seal thing. That's a minor consideration. Ross Pink got around the problem by using grease instead of oil. Alternatively, it can be dealt with by a simple drainhole drilled in the adapter plate, vertically down from the hole where the motor shaft passes through it.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).
Sorry, PlanB, you asked me not to mention that figure. Slip of the key 
