A little identification help please!

Here are some images of my block. Please let me know where an I'd chart exists to breakdown my block numbers?

Do any of the more knowledgeable than me know who makes a set of main journal caps that fill the entire void between block sides to provide a solid web for support?

Thanks folks!

View attachment 1715111714 View attachment 1715111715
That casting number was used between 72 and 78. I don't know about the 4 bolt mains. I'm sure it can be done by a top notch machine shop.