I know this is an easy one for you gentleman; could
ASTM A105 be used as a replacement for ANSI 1026.
The 1026 material (normalized forging)is on an 18 week backlog, engineering wants to see if A105 would make a good replacement. The forging requires yield and CVN restrictions (nothing high).  This material will be reviewed by surveyors, and I need to make sure this is
acceptable. I believe the 1026 is under the specifcation
ASTM A830 (not sure); if not A105, what would be equivalent
to 1026 material? Any advise would be helpful.

Oh....we do not have a Metallurgist or Welding engineer on staff.

1026 is the only thing equivalent to 1026, and then only sometimes.*
What is the application?  What codes apply?  How is ASTM A830, 'Standard Specification for Plates, Carbon Steel, Structural Quality, Furnished to Chemical Composition Requirements' related to your product?
*As 1026 per A830 has stricter limits on P & S (0.035 & 0.04) than does standard 1026 (0.04 & 0.05 wt%, respectively), it should have improved impact properties.

Comparing ASTM A105 'Standard Specification for Carbon Steel Forgings for Piping Applications' to the AISI 1026 chemistry is like comparing an iced cake to a grade of flour.  
Why was 1026 specified? A higher carbon content may require changes in forging or heat treatment or any subsequent welding.
   
ASTM A788 'Standard Specification for Steel Forgings, General Requirements,'  
A266 'Standard Specification for Carbon Steel Forgings for Pressure Vessel Components' or
A765 'Standard Specification for Carbon Steel and Low-Alloy Steel Pressure-Vessel-Component Forgings with Mandatory Toughness Requirements' are perhaps more relevant specifications for a forging.

The 1026 forging is used in a rotary table assembly for drilling, it is being welded to A36 and A516/70 plate; ASME IX is the code used. As far as ASTM A830 is concerned, that was incorrect. Where can I find chemical/mechanical information on standard 1026?  

I believe engineering is just looking to find something
(A105) that can cover the mechanicals (min. yield 36,000 & CVN 20/13.3 ft-lbs. @ -20 C) and weldability, the
chemical compostion was probably overlooked. So far no material has been ordered in place of the 1026.

Grade 1026 appears in numerous SAE and ASTM standards; kenvlach listed some of them.  It will have slightly different allowances for composition depending on the standard, while some will specify mechanical properties and others will not.  If your engineering specification says "ANSI 1026" or "AISI 1026" or "standard 1026" then it is incorrect.  You need to reference a proper standard (ASTM or otherwise).

TVP,

I had a feeling that ANSI 1026 had to derive from
some standard, I asked the engineer to what standard
did the 1026 come from, he didn't know. Unfortunatly the engineer who designed this rotary table is not with us any more.