Use the wrong tubing and break the casting trying to get the peen tool through the bore. Don't ask how I know that.
That’s true about the tubing. If the OP isn’t comfortable with making a tubing choice I can look up what I use and give him the part number. The other thing I forgot to mention is that even after peening the lifter won’t fit in the bore without binding (probably). So I always take a paper roll and polish the tube where it breaks through the lifter bores.
Also, I stopped using a press fit on the tube years ago. It should slide right in. Once you peen the tube it can’t come out. It’s much easier and cleaner to slip fit the tube. Even if it’s a .010 slip fit. Pressing the tube in with even .001 press is a PITA with about a 10 inch tube with that thin wall.
