I had one eye-opening experience when I lay beneath the car checking the alignment carefully. I noticed that two of the flange ears were further from the face of the guibo than the other two. Crap, I thought. This was a used Craigslist shortened driveshaft of unknown provenance. This seemed like clear indication that the flange wasn't welded on straight. I looked at it and looked at it, though, and couldn't see any wobble in the flange itself. I thought maybe two of the ears were bent. I was about to take it out and try and beat the ears into submission with a small sledge when I thought... maybe the guibo face isn't flat. I took some White-Out and marked the two flange ears and guibo holes that were out of alignment. Then I took the bolts out and rotated the flange 180 degrees, using the white marks to verify that I was doing it correctly. Sure enough, the white-marked flange ears now looked fine, and the white-marked guibo ears were slightly misaligned. The take-away message from this is: get it as close as you can, but the guibo is a piece of rubber, not a machined surface. If there is asymmetry as you spin around, it is more likely to be in the guibo than in the driveshaft. Be certain which one it is before you do anything drastic.
I tightened up the guibo and bracket bolts and thought, whew, tough part is over -- just bold on the headpipe, connect the exhaust, and you can drive this baby. I began connecting the headpipe, and immediately saw that I had a problem.
My headpipe has an oxygen sensor that connects to an air/fuel meter (indispensable for dialing in the Kugelfisher injection). It protrudes from a bung that's welded onto the headpipe. The recommendation is to have it at a positive angle relative to the horizontal so moisture doesn't accumulate in it. The location and angle I chose were selected when the four-speed was in the car. I hadn't given a moment of thought to how this would interact with the 5-speed... until now. It was clear that the O2 sensor pointed right at the transmission support bracket. Would it hit the bracket, or clear it? I gently tightened the three nuts where the headpipe bolts to the manifold, waiting to see whether that would pull it into the bracket or away from it.
Once the headpipe was tightened, the O2 sensor either just clears or barely hits the bracket, depending on whether you're a glass-half-empty or glass-half-full guy. In addition, the clearance between the bung and the U-bolt clamp that bolts to the bottom of the transmission is also tight (again, the bung location was chosen when the four-speed was in, when that U-bolt clamp was 3.6525" forward of where it is now). Given the choice of cutting the notching the transmission bracket (you can see the magic marker outline of where I'd need to cut), or buying a new headpipe and welding a new bung into it in a different place, or buying a different transmission mounting bracket, or just mounting it as-is...
Well, no surprise which is my default choice. It's all bolted up and ready to go. I'll give it a whirl and check how things look after a few drives... as soon as it stops raining.
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