Yes, I noticed that it says that the input impedance is pretty low at 3 Mhz.
On the other hand Heathkit many times comes up with checkout methods that don't require a lot of other test gear. There may be adjustable parts that they pre-set however, so I would not turn things until you have the manual.
I found a place to get the manual, not free but probably your best chance of getting one.
https://manualman.com/index.cfm?CFID...461B60C3A15E25