Just a note with the 1.3GHz-ish counters. They tend to have a 50 ohm termination required as that's well into "scary transmission line territory" so you'll probably have two inputs, one a high impedance usually up to about 200MHz (if you are lucky) and a 50 ohm terminated one up to 1.3GHz. The terminated one requires more power to get it to count so you will most likely have to rely on the lower frequency input. They are usually ok with a 10X scope probe attached to the high impedance input if the level is above 10-20mV or so.
However you may still have problems with the sign gen - those old ones have quite a high output impedance and low power output so it might still not be enough to drive it still with an IF can and counter attached. I had the same problems with my (relatively modern in comparison) transistor based Solex which was frustrating.
I would, to save the above problems if you can:
1. Fire up the generator and leave it for an hour (they drift like mad).
2. Mark up the generator with a new scale measured by your counter with the common IFs you will use.
3. Disconnect the counter and stick the generator at the desired IF.
4. Use a 10x scope probe or VTVM with diode probe to peak each stage.
A counter is a relatively new invention really. I think my father aligned them with a Heathkit VTVM and uncalibrated Heathkit RF-1 and did ok!