Since I destroyed a lower rod needle bearing after break in (and you’re right it’s not fun $$$) I would suggest following a few tips stated.
1) use an old plug and run the mixture rich. The plug’s junk afterwards but you’ll not stick it
2) Don’t use a 98 needle
3 heat cycles is enough as long as you let it cool for a while and ambient isn’t necessary just 10 minutes between.
I will say that Welch and Vito haven’t blown an engine and neither did I so do it right and it’ll treat you right too. I can’t emphasize being rich enough. It’ll only foul the plug. Once it’s broke in you can let the engine clean itself!