"A high horsepower intake" doesn't exist if you don't change a bunch of other things to compliment it. Especially the 2bbl carb. You MAY see a marginal improvement with a Performer style dual plane intake but don't expect it to turn your 140HP small block into a fire breather. Not gonna happen.
You would be better off to do a good tune-up on the stock set-up AFTER you get your new exhaust on it.
If you want to see some bang for your buck yank the 305, as is, and slip in a crate 350 or 383. Slap some 305 stickers on it and go hunting...
A 700R4 OD trans is pretty much a bolt in and it will help off the light response and increase your MPG while cruising...
Mark