That is a nice block!
My C3 Top Oiler needed a sleeve to go to 4.25 from standard. It's .030 now and I hope it's good for .040. Suppose I should do another sonic check on it...but I'll probably run it regardless.
I have the Ebay $100 sonic checker. Sanded the pick-up oval. Check between the top of the bores and match to my calipers first, and do it every time when you move to another cylinder.
Mine seems to be stingy...or...all my blocks are runable but thinner than I'd like.
I use "personal" lubrication with my checker.
