Had a pretty productive day today. First off, I got the engine running much better. It will now fully rev up. The issue was not the emulsion tube. Turns out the 0.42 jet was way too lean, so I drilled out the stock jet with a 1/16" bit and it worked perfectly. Max RPM I recorded was 5280 but it has more in it, I just didn't want to rev it too high without a load on the engine.
I also got the floor pan/brush guard made. I used 1/8" thick ABS plastic sheets. It's very light, durable, and easy to work with. I'm going to cover the top side of the floor with skateboard grip tape to provide extra grip on the floor so my feet won't slide around.
I also drilled out my spindles/pitman arm to take a 1/2" bolt for extra strength. My one concern is that now the hole in the pitman arm is too big and it will crack (which would be very dangerous at speed), so I'm going to weld around the outside of the arm to add more material and grind it smooth.
Finally I began making the steering linkages that will be put in place to reduce bump steer. The larger holes will be the pivot holes and have a bronze flange bushing to prevent wear. The smaller holes are where the tie rods will connect. I drilled two holes so I can adjust steering angle/effort if need be. I still need to round out the edges, but they are mostly done. The dots on the outside of the larger hole are just there to remind me which one is the left/right one after I paint it (dot faces out from the buggy).
All in all this project is going pretty well. It's far from perfect in terms of absolute precision but this is my very first ground-up project and I'm building it with basic tools. I'm kind of using KGN Metal's buggies (search them on YouTube) as inspiration. They look rough but are very functional. Anything that breaks can be fixed fairly easily. Function over form is the name of the game here.