Can a handi rifle be barreled for the 25/06 or is this only for the ultra?
Yes, depending on when it was made, there's no difference in Ultra and Handi frames.
Do they offer the 357/44 for the handrifles or are they only putting these on the SB1 as the add said that the guns built with these could not be chambered for any other centerfire cart.?
The SB1 rifles are Handi-rifles, just on SB1 frames, they can only be fitted with other shotgun barrels, no other rifle barrels. Any SB2 frame made since 1987 can be fitted with the 357 or 44mag barrels, with possible exception of the '96-'99 frames which isn't confirmed yet.
Who makes the syn. stocks for them? Are they all marked H&R or black or NEF
Choate Machine has made them in the past, I suspect they make the new checkered syn too, there are no NEF marked rifles anymore, the only NEF marked firearms produced now are the imported shotguns, they may now be marked H&R too.
Are the new rifles (2009) rifles marked as NEF or H&R ?
H&R only, NEF is defunct for all practical intents and purposes, it's not listed on the website anymore except in reference to the imported shotguns.
Is there any receivers that cannot or that they wont fit barrels to made by H&R or NEF?
Wesson & Harrington frames, some '96-'99 SB2 frames(not confirmed yet) pre '99 SB2 frames can't be fitted with high pressure *marked barrels.
did they discontinue the muzzleloader accessory barrels?
For now until they're modernized, see Huntsman/Sidekick sticky.
Tim