The first GPS antenna bracket made has issues. Not wide enough for the GS35 antenna, and a bit short. Created a new bracket, at about 3.25 inches wide. I used WDG clamps to attach to the top of the engine mount, and two AN bolts to attach to the firewall with nylock nuts in the baggage compartment.
Used an old non-WAAS antenna to locate the holes since it had the same call-outs for the (4) screws and the BNC connection.