Okay, Howard, this is a common problem with a twist (the hat channel). Here's my thinking

Your Concerns are Valid
37 lbs is Significant

That's a heavy fixture to hang solely from drywall, especially with the added leverage of a swag.

Drywall Age and Condition

20-year-old drywall can be brittle and more prone to failure. You're right to be wary of unknown provenance.

Hat Channel Complexity

The hat channel system adds another layer of uncertainty. You need to ensure whatever anchor you use doesn't crush or distort the channel.

Liability

If the fixture falls and causes damage or injury, you could be held liable if you installed it knowing it wasn't adequately supported.

Possible Solutions (in order of preference/likelihood of success)


Find the Hat Channel



Investigative Work

The first step is to locate the hat channels. Use a stud finder that can detect metal. They are typically spaced 16" or 24" on center.

Anchor to the Hat Channel

Once you locate the hat channel, you can use metal drill screws/TEK screws that are designed to screw into metal. You'll need to select a screw length long enough to go through the drywall and securely into the hat channel. Make sure the screw head is large enough or use a washer to prevent it from pulling through the drywall.

Pre-Drilling

Pre-drilling a pilot hole through the drywall and into the hat channel is highly recommended.2.

Bite the bullet and either move the box or install blocking.Less Desirable Options (proceed with extreme caution, and only after thorough inspection)



Heavy-Duty Toggle Bolts (With Stronger Toggle Wings)



Upsize Everything

If you are set on using a toggle bolt, you need the largest, heaviest-duty toggle bolts you can find. Look for ones specifically designed for heavier loads.

Reinforcement

Consider using a fender washer (a large, flat washer) between the toggle bolt head and the drywall to distribute the load over a wider area.

Test It

Before installing the fixture, hang a sandbag or other weight (slightly exceeding 37 lbs) from the toggle bolt for a few hours to see if it holds. This is crucial. Watch for any drywall sagging or cracking.

Still Risky

Even with these precautions, this is still a less-than-ideal solution, especially given the weight and the swag configuration.

Important Considerations



Communication with the Customer is Key

Explain your concerns clearly and honestly. Tell them the potential risks of hanging that much weight from the drywall and that you can't guarantee its safety. Present the best options (finding the structural members or moving the box) and explain why they are the preferred choices.

Code Compliance

Check your local building codes. There might be specific requirements for ceiling fixture support, especially in a multi-story, fire-resistant building.

Documentation

Document your conversations with the customer, the options you presented, and their decision. If they insist on a less-than-ideal solution, get it in writing that they understand the risks and are accepting responsibility.

Consider a Disclaimer

In your contract or invoice, include a disclaimer stating that you are not responsible for any damage or injury resulting from the fixture's weight or the chosen installation method.

Ultimately, you need to be comfortable with the safety and stability of the installation. If you're not confident, it's better to decline the job than to risk a failure. Your professional reputation and your customer's safety are on the line.Good luck, Howard! Let me know what you decide. Flag for review