Everything is fixed!

I had previously checked all of the connections but upon finding the bad ground on the MAF, I rechecked the two main connectors near the battery that join the inlet manifold loom to the engine bay loom. When I actually pulled one of the connectors apart and examined the pins on the male plug, I noticed that two of the pins were not as long as the others. I used pliers to pull the pins out further and clipped them back into their normal place. Plugged the male and female connectors back together and went for a drive to find everything is back to normal now.

Glad it was a simple fix, but having an SSMI reader would have greatly assisted me in making the discovery much sooner. I've ordered an FTDI TTL converter and will be making my own cable shortly.

Have promptly done an oil change too to get rid of the old fuel-diluted oil.

Thanks everyone