Hmmmm. Doesn't sound like a factory switch. Made in China???
I'm guessing the wires and plugs all matched up ok?
Not sure if the 260 switches are the same as a 280 (your's is a '78 280 according to your sig). You might want to verify with someone if the 260's are different.
I know alot of the stuff for a '74 260 might work for a 75-76 280, but alot of stuff for the 77-78's aren't interchangeable with even the 75-76's... let alone a '74.
Just a though...
Most of the old 80's GM (and other) speedometers only went up to 85 mph. Personally, I like speedometers that go 140 to 160, even if I never drive that fast (often). I had a '78 Pontiac Trans Am with the 400 engine and 4 speed. The factory speedometer only went to 100 mph. I could peg that with no problem in 3rd gear, and have the needle go past that a couple inches when in 4th gear.
To each their own
To be safe, make sure ALL your rubbers are good (radiator & heater hoses, vacuum hoses, tires, and that thing some guys keep in their wallets in case they get lucky)
I loved my Toyo's. Good grip, nice tread pattern, but they did seem to wear out fairly quickly. I had Federal's, which seemed to wear forever, but not the grip like the Toyo's. I probably will go with BFG's next.
I had the exact same thing happen on a '78 I owned about 10 years ago, sticky goo and all. Got the module from U-pull wrecking yard for five bucks. Problem solved. Cheap.