Cheapest way to do this is to buy an 8-9-10 speed 130 width wheelset, an 8-9-10 speed cassette with max cog size of 28, and an appropriate chain for the number of speeds. Assuming this is a Shimano equipped Ironman, set the shifters to friction and have at it. All of those Shimano components are compatible and work well with 8-9-10 speed setups.
If you want indexing, purchase a set of downtube shifters in the same number of speeds as the cassette and chain.
If you want to go to STI's, then likely you will need a later FD as well since the 105/600 ones found on 80's Ironman bikes were not intended to run indexed (note: this MIGHT work, and would be worth at least trying).
If you have a later Ironman with non-Shimano components, perhaps others here can give you advice on how to upgrade it.
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