It's a shame no one ever invented a central communications system with endless databases that anyone could look things up on just by typing in some words, like a devices part number, or something in order to find its exact manufactures specs and recommended base circuit diagrams plus any other technical info as well.
Not to be rude but, if I I'd be GD embarrassed about the excuses you give for doing things the way you do and have done for how many years now on this site relating to these induction heaters of yours?
You say you have the IGBT's so obviously they have a part number you can look up their data sheets with to which those said data sheets will give you the exact numbers you need to calculate the worst case thermal dissipation values you can have given your input voltage, amperage and switching frequency to which from there figuring out how big of heatsink you need can be done.
You've built a big ass Telsa coil at one time that worked (if I am getting things right) so obviously as a past engineer you know how to do basic technical math and design so finding the numbers you need and the rest of the data for any other related items and coming up with basic designs that exceed those minimum working requirement values should be like breathing to you.
So why isn't it?