Hi Bob.
A scope is a terrific piece of test equipment, and can do many, many things. For audio use, you don't need anything terribly fancy, since you'd probably never measure anything beyond 30kHz in the audio domain. The MHz scopes are more for radio use - hams, for example, need a scope that will run out to 100 MHz to test their transmitting/receiving equipment in the high radio bands. You will need at least two channels so that you can do an XY pattern for measuring head azimuth. In addition, you'll probably want a sine wave generator to set recording levels, checking record EQ, bias and so forth. Finally, a spring scale to check brake tension (the kind sold for grade school science classes are ideal, since they generally measure in both Newtons and grams; avoid the fish scales).
BUT - if you have a computer with a good sound card, you can get software to act as both a sine wave generator and as an audio-frequency 'scope. Software is likely MUCH cheaper than a real scope, and for aligning a tape machine, the software is probably good enough. I use my iMac for these functions with ToneGen (sine wave generator) and SignalScope software. I've set the azimuth on my heads with Signal Scope, which also will read voltages and db to a set reference. I'm sure similar software is available for the PC side, although the nice thing about the Mac is that the software guys know exactly what hardware is being used and what the specs are on it. Can't get the computer to be a spring scale, though <grin>.
John C.