I did a search and there was a tread on 10 vs 11 speed but not on 9 speed.

The bike: 2006 Trek T2000 tandem
It originally came in 9 speed ultegra all around ultegra triple tandem.

I bought the bike used and it had been converted to 10 speed components, shifters, front and rear derailleur but NOT crankset

I have a lot of trouble shifting the triple chainring, one of the problem I discovered was that the crank being a 5603 had 53-42-30 chainring but they put a 6603 front derailleur and the cage does not work well with those gearings, so I put 52-39-30 rings, helped some but we had the occasional chain suck problem, chain sticking between small and middle ring and on a tandem when two are pushing, its not fun.

Now I don't feel like changing crankset to a 10 speed tandem setup, rare and expensive.

I could have the spyder tabs where the chiainring meets them machined to take out material to the spacing would be the same as a 10s triple.
Would that work?

if so, anybody know the spacing that a 10 speed should have between rings? the thickness of the big/middle ring tab would tell me that and the distance between the inside of the small ring tabs and outside tab.

Am I on the right track? any other options? its a 6503 crankset ultegra octalink.

Thank you

Edit, corrected part numbers