Don't think you'll get away with welding any way with how thin the roof is. Be like a banana after its done. Let me know what solution you come up with, i need to get rid of mine to meet the regs for racing. Was going to re-shell :/
I've got Wiseco pistons aswell bud. Like you say, the tapping is nothing to worry about, they are known to be noisey. Thought I'd mention it incase any buyer was unsure!