I ran a mini express mushroom in a 426 maxwedge block. I had the bottoms of the lifter bores relieved...... and it was totally unnecessary.
I was very inexperienced with that much cam at the time, and the mini lost a few lobes (way too much spring pressure, poor breakin).
I wish I hadn't thrown the lifters away, they could have been saved.
IF I still had a mini, and IF I had a block to run it in, I would SURELY mock up the cam and lifters to see if relieving is necessary in that particular block
Edit; I also had the bore relieved deeper for the big exhaust valve of the max head, which was also unnecessary. .070 over (to standard 440) had plenty of bore size for the 1.88 valve, to .750 lift.