I’d dive in and fix it. Gonna be a long expensive project if something little like this requires a tow truck and $150/hr to diagnose and repair.
Can help you start diagnosing if you’d rather spare the tow.
Knowing this is an old running driving vehicle where basically everything is either original, unverified or of questionable age and competency, start with the easy stuff.
See if the starter is drawing any power. Not likely if you didn’t hear the solenoid click. Lights will dim when you turn the key of the starter is pulling power.
If not, first jump the solenoid on the starter with a screwdriver. If no big sparks and no crank or at least click then no power to starter.
Inspect/wiggle/or just replace battery cables if they’re old and crusty.
Check for 12V at solenoid when turning key to crank.
While it’s possible it’s the ignition switch (jumping the starter with a screwdriver will allow it to crank w a bad ignition switch), or associated wiring from the steering column to the starter, it’s much more likely something under the hood.
Bad cables bad ground, bad solenoid trigger wire, bad starter solenoid, bad starter motor.
For the cost of the tow and the shop for just a couple hours, you could buy all new components and the tools to test and fix it.
Tryin to help.
I feel bad for folks like the guy I bought my C10 from who handed me a stack of over $15k in receipts, not including the purchase price of the truck when he bought it (although I think his dad gave it to him).
Then I handed him $7k and drove away with it.
Idk your budget or how you plan on distributing that budget. But The difference between diy and someone else doing the work is orders of magnitude different. Plus while this is a sentimental build, the ROI in Suburbans is far less than pickups. Many things cost twice as much or more like restoration things, interior, paint and body, because there’s more to replace or paint. Mechanical and drivetrain is the same $.
But apples to apples, Burbs are worth considerably less than a comparable pickup.
Only hope of not being waaay upside down is at least doing the simple stuff yourself.
Best news is, you have a plethora of old squarebody mechanics and fanatics here to get help from.
Now go get ‘er running!
