NOT that big of a problem. I am currently working the kinks out of auto to manual. Most of the Electrical is in the bag, just reroute /splice about 6 wires.(All the auto trans controls are buried in the engine harness connected to the TCM, those wires just get cut away.) You may have to reflash the BCM?, this is a point I have yet to address, BCM differences? or source one from a manual.
A Wilwood brand clutch pedal set up? They make several types, I feel sure one of their designs would retrofit to a Goblin easily, you'd probably have to cut down that huge auto brake pedal but you can use a cutter wheel can't you? I discovered the hydraulic connection bits today! Using a little ingenuity and a little cash the pipe set up comes in around $70.
Shifter cables, I found a source just a few minutes ago!(been researching for weeks. I am up against a deadline of June 9th.) Or get them from Goblin, theirs are made to measure!
Manual shifters, I've got plenty of ideas and shifters sources from Goblin's basic reversing OEM to scrounged and modified to DF's custom built unit. It all depends on how fancy you want to go.
F23's are out there, the special ones out of HHR have final drive of 4:11(drag racer gears)
I suggest you buy the automatic Goblin runner and convert to manual as time and funds allow! I've got all the research and I'm not keeping it secret! I'll gladly walk you through it. These Machines were made by humans and can be modified by humans. If you have the gumption, this Forum has your Guides.