Tube compatability question

I have a 30w chinese amp using 6L6G tubes. I was looking to buy some 6L6GC tubes as replacements. If I understand the info I'm reading correctly, the 6L6G isn't as heavy duty the 6L6GC and doesn't replace it. But I'm wondering if the heavier duty 6L6GC can replace the 6L6G.
The tubes very likely could be your weak link.
Also, what gain tubes are in there? 12ax7? Replacing those may make a drastic difference.