On the fuel pump... SU pump or aftermarket? (EDIT: See footnote at the end... sorry)
On an aftermarket pump, wiring it backwards may let the white smoke out and you may create a non-operational pump. On an SU pump, no... you don't reverse the wires on the pump because the body of the pump is an earth connection. Yes, a separate earth wire may run to the pump... but the pump body is still an earth connection. Do not reverse the wiring. Early SU pumps did not have any components to protect the pump's points, later a capacitor was added. On even later pumps the capacitor was replaced by a diode. The capacitor was not polarity sensitive, the diode is. So, what you DO have to do is remove the plastic cap on the SU pump and (unless you can tell the difference between the diode and capactor) reverse any points protection device that is located under the cap. See the link below to Barney Gaylord's MGA web site and his pages on the SU electric pump. It includes a discussion of the electric pump, the capacitor and diode.
http://mgaguru.com/m.../fuel/fp100.htm
The joining of the two wires at the dynamo to each other is not the end step. To flash the dynamo those wires have to be tapped to the battery connection to change the residual magnetic field inside the dynamo. Touching the dynamo terminals to each other does not do this... you have to make a battery connection also. See the link below for steps on flashing the dynamo to convert its polarity.
http://www.minimania...trical_polarity
Note that most of your car's electrics will be fine. HOWEVER, you do have to switch the coil low-tension terminal connections and you have to address any aftermarket electrics (such as a tachometer) that may have been fitted.
Someone is bound to post: "Don't forget to change the polarity of your gauges or they will read backwards". The gauges are not polarity sensitive so do not make any changes to their wiring (except for aftermarket tachometers as mentioned above).
An overview of the earth conversion is discussed in the MG link below. The Mini is not differrent except that the MG came with an electronic tach.
http://www.mgexp.com...eg-convert.html
EDIT: SU pump with a blue cap. Those are typically the German aftermarket pump. I am not sure how or if you convert their polarity. It could be replacement is required for negative earth. SU pumps typically have the black cap as mentioned by Grumpy. For at least a while, SU/Burlen was using different colored tape near the black cap to distinguish between positive and negative earth versions.
Edited by dklawson, 23 July 2014 - 12:31 PM.