Miitch's Time-Trial-Tandem

spacers to move the timing rings inboard by 2mm, because the 1R8 final drive chain has very long pins

So, with small spacers and long chainring bolts you think 'd be able to get away with it? - I think that would be easier, because changing the timing chain also means changing the timing rings.

So, with small spacers and long chainring bolts you think 'd be able to get away with it?

I didn't even use particularly long bolts, just the stock ones from the FC-S500 cranks. The drive is provided by friction between the rings and the spider, so as long as there's enough thread engagement to support the required bolt tension, the tubular nuts don't actually have to engage in the final drive ring. It's a clutch, not a pin drive.

The problem you might run into is crashing the timing chain into the chainstays if you try to push the timing rings inboard. Depending on where things are tight, you might have to push the final drive outboard too/instead, and then fix the chainline at the hub if necessary.

Managed to get some spacers to space out the big ring today and it worked, however the chains are now maybe too far apart and it makes for a slightly funky chainline at the rear. I think I need slightly thinner spacers and then it will be sweet.

Please excuse my awful photography skills.
This photo shows the gap between the two chains:

This shows the set up with the spacers in place:

I think I need spacers half the width of the ones I bought. Even though all the bolts are tight the chainring still seems to have some side to side play (right/left play). I'm going to get some new chainring bolts and see if that helps the issue since the current ones are old and a bit gunky.

Has this been raced yet

Sorted out a no-name left hand crank, so it's usable at the very least.

Since I ended up buying an 8mm drill bit for a different project, I drilled both the front and rear, despite it probably not being very sensible. Once I started drilling the rear brake bridge it was a lot beefier than expected, same goes for the front to be honest. I'm fairly confident everything will be ok...

Only issue now is I didn't think about caliper drop.

Think I'll have to go for 57mm drop calipers, hopefully I'll be able to order those tomorrow. I'm also going to try a thinner chain for timing chain, to try and get a decent chain line. Will update tomorrow.

If you don't want to replace the whole caliper, you can get deeper drop brake blocks which add some drop. A friend who owns a bike shop recommended them to my girlfriend when building up her touring bike.

I had thought about these. However that with the wheel only halfway back in the drop out, so if I was to change cog on the rear then it still wouldn't be enough

I've changed the timing chain for 10speed and it is tons better. The bolts on the eBB are imperial (and I have no imperial tools) though so it's a bit too tight. The chains still collide, unless you push the back chain across. So I still need to space the rings apart by less than 1mm to give me decent clearance. I moved the front ring to the inside of the spider but that's ruined my timing chain line, so I need to move that back. Then finally to fix my back chainline, I think I'll have to fix it at the hub as @mdcc_tester suggested.

Will a 130mm fixed hub have a wider body than a 120mm hub? Therefore sorting out the back chain line

Bad timing chain line

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If you squint and tilt your head you can see the slight difference in clearance between chains depending on if I've pushed it over or not

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Will a 130mm fixed hub have a wider body than a 120mm hub?

No, just a longer axle with some extra spacers.

What's the pin length on your final drive chain? You can get down to 8mm with the flush riveted KMC X101, or even swap to a 3/32" sprocket and use the 6.7mm wide X1

Boost (110×15) hubs with 6-bolt sprockets are the way forward for 47mm chainline to match the outer ring of a road double, they actually have wider spaced flanges than 100×15 hubs, although the latter build up symmetrical if you shift the hub 5mm to the right to get the same chainline.