[TheForge] Power Hammer Dies... revisited

[RW]

I want to make some flat power hammer dies that will have a square hardy
hole in a longer  bottom die to the right of the hitting surface to hold
tools.  I only want to make these once.  I noticed that my current H13 top
combo die has developed some small indentations from hitting tools.

The new dies will be welded to a mild steel plate which will be bolted to
the anvil face.  My welder is AC only.  Do I need a DC welder to get a
reliable weld?

I know this is somewhat of a rehash of an old thread but any input will be
appreciated.

I can buy annealed H13 blanks from my local steel supplier for $110.
Cutting the square hole is about $100.  Heat treat is $95.  Would welding
the annealed H13 to the plate and then heat treating, normalize the welding
stresses?

Would anyone prefer 4140 or 4340 over H13?  Why?  How would you handle these
in the above scenario...professional heat treat?

Thanks in advance.  RW Swisher