A bit of a late reply, but I hope it is still of value.
The 1854-0441 was used as Q4 on the A17 boards for instruments with serial number prefixes in the range 2410A to 2532A. It is a general purpose power NPN transistor in a TO-3 package. In later instruments it was replaced --- without changing, to the best of my knowledge, any of the surrounding components --- with a TIP41A transistor which comes in a modern TO-220 package.
Thus, if you need to replace the 1854-0441 either go for a TIP41A (in which case you will need to accommodate the different footprint and replace/modify the small heat-sink), or look at the TIP41A specs and locate a reasonable replacement in a TO-3 package, which should not be hard.? Note that even though these are power transistors they are dissipating well below their rated maximum power in this circuit as they are mounted on tiny heat-sinks.
