It's on bitsavers in pdf/sgi/iris/firmware
There's a bootload prom as well, which tries to boot from something - network or disk, I'm not sure.
Also - the Sun-1 monitor is not the same (earlier?) than one described in pdf/sun/sun1/800-0345_Sun-1_System_Reference_Manual_Jul82.pdf (does not have "B"oot command etc.) and diag roms are also different
The 1400 CPU board is a Sun-1 layed out to fit on their larger size Multibus cards. It is probably trying to use the DSD MFM disk controller or a interlan multibus ethernet board.https://preterhuman.net/forum/index.php?topic=102.0
has one version of the hardware faq
Sun Microsystems, Forward, Callan, Codata, etc. etc. did their own hacks to the SUN boot proms adding different disk support, for example, so I'm not surprised the commands are different.
You will find lots more variants in various manufacturers directories on bitsavers