Hi,
I'd like to know if SAEJ442 permits to weld almen blocks to form an Almen Fixture. If not, can I manufacture Almen blocks with additionnal holes and/or tabs that couls be used to fasten them to the fixture?

SAE J442 does not limit the method of attaching test blocks. Welding is frequently used method.
J442 is the revision process now to add a statement allowing one or two extra threaded holes for mounting as long as the holes to not protrude into the strip mounting area.

Don't go crazy with the welding otherwise you may compromise the hardness of the test block. The best method would be to heat treat your entire fixture once complete.

David,
You should also be careful that the Almen holder does not warp due to the welding. Also, you might be required to prove the flatness of the working surface during an audit so you might want to plan ahead how to verify the flatness while it is welded into place.