What diameter are the exhaust valves? What about head casting numbers?
All the Chrysler 300 motors before 1962 had solid lifters and those type adjustable rocker arms. All the letter series 300 motors had them until 1964 also I think the 1964 300 letter cars used the six bolt valve covers and the later style rocker arm pedestals cast into the heads also
You may have gotten very lucky

So other than the bore notches, is there any "real" difference between a MW block and a 413 out of a New Yorker

62 MW blocks, ive seen there are also 2 bosses at the rear of the intake area, look similiar to water pump housing bosses, but of course not open. only HD blocks had those from what im told

I've not seen a lot of original 413 M.W. blocks but I'm going to say none of them used the H.D. industrial blocks to start with
I have used a 413 H.D. block to replace a original 413 passenger car block in a original 1962 Dodge M.W. Dart, the original 413 block in that car(not sure if it was the original proper block or not either) was already bored to 4.240 and it did not sonic test well either
I had the 413 H.D. block bored too 4.250 and had Diamond make a set of reverse domed pistons to make 9.4 to 1 compression ratio so the customer could drive it on the street with CA pump swill back a long time ago in the mid 1990s
I am using a 1972 413 H.D. truck block in my 1963 Fury to mess with some of the local car show expert crowd
I'll tell them a story like I know what I'm talking about
I'm going to tell them it was a rare factory option police pursuit car or something similar, it has a set of 440 Source heads painted the Mopar green and a 4.150 stroke crankshaft with a little over 10.3 to 1 compression so I'm hoping it will make north of 525 HP