It sounds like LS was your intention before you bought it. Personally I prefer old rigs to keep their integrity. Does that mean only an engine and transmission available in 1965? No. There are plenty of setups out there that will drop right in that 65.
I will never be a proponent of ls swaps in any old vehicle.
My passion is in 60s series trucks. Should you keep the 283? Not necessarily. Same for the 3 speed. We provided info about other directions to take, you had ls in your sights from the start.
In the end it's your truck.
Saying it like it is, and other's opinions not aligning with your intent, does not make the site bad. We're all the same people, just older and wiser, and some new members. You want to get beat up on a forum, post this same information you shared in this thread over on the Stovebolt forum.
Some of us may not agree with you, but we'll watch your project progress.