Doing a MINOR amount of research on the gigabyte web site (why didn't you???) yielded the following information...
1. Processor support listed as "AMD Athlon? 64 up to 3400+ and higher" so the 3500+ SHOULD be good...
2. From the look of the cooler, it will fit the same as a stock cooler. It's not any larger than the other coolers that go for the Athlon64's.
3. Also from the site... "Heatsink Dimension 83 x 89 x 93mm" If you have more than that for room around the processor socket, you should be fine.
Next time, do at least some checking on the manufacturer's site before posting questions like this. Hell, they even include pictures on the site with labels for the different processors it's made to work on... How much easier can they make it for you???
If you still don't get it, email gigabyte and ASK them.