What year engine? Keep in mind the pre/post 2009 is year break for vvt or non. I know I have a takeout hellcat cam, and 6.4 valve springs on the shelf. PM me if interested. Literally brand new takeoff parts.
Sticks in my head that 6.4 valve springs won't work on 5.7 heads. I know for the 6.4 cam swap I will do on my 5.7 I had to buy 16 of the 68277306AA valve springs.
Can't say for sure if it is an issue with the Eagle heads, or if all 5.7 heads, nor if the 6.1 has the same problem. And not sure if it is length of the valve, or the valve spring pocket that makes it a problem. Only that I read that a 6.4 cam swap on a 5.7 can't use stock 6.4 valve springs.