Have you tried just simply trying to boot from your OK prompt with:
That "disk1" name is customarily already aliased and hard-coded in a SPARC system's firmware.
Here's a link to the OBP 4.x Command Reference Manual:
Save a copy and perhaps even print it out for future needs.
The following can get you to a quick-reference chart of commonly used OBP commands:
Save a copy of that as well.
(Your V440 was designed to have OBP version 4.x and I found both of those links with a Google search on "OBP 4 manual".)
For what you have described in your initial post, there is probably no functional difference. The "sd reference is from the device pathing along the PCI bus and the "disk" reference is from the OBP aliasing.
Make a choice and use it consistently. That will help you in the future to remember what you've done.