Yours is not a Camber 3.5, it is the original version that had the Rega designation. Your model is a predecessor to the 3.5 that was designed at the NRC (National Research Council) in Ottawa under Dr. Floyd Toole who now works with Harman/JBL.
Side by side, the 3.5 and yours would share the family sound, they are very close. The 3.5 was commissioned by the CBC as small room studio monitors. Camber was later sold by Edon and the manufacturing plant was moved to Montreal. Out of the blue, the owner left and was never heard from again, causing the demise of Camber.
Just enjoy the Regas you have, they are that good. When I sold them (they went for around 300$ a pair) and a customer wanted an upgrade, I would suggest looking past the 1K mark as a viable upgrade. We often suggested the Harbeth SLH 5 mkII that was designed by Dudley Harwood. Those listed at 1500$ at the time.
You can change the binding posts in the back if you wish to insert banana plugs. Next upgrade could be the crossover caps if needed and also adding a 2x4 glued to the back of the enclosure and rest it on the woofer's magnet with damping matrial (rubber, cell foam, mortite used for window sealing...) if and only if your Polidax woofer doesn't have a vent (a hole on the back of the magnet) in the middle of the magnet.
As they are, they are still amazing for what they cost and will give many modern speakers a run for their money. At 10$, you can't beat that.