Z head and O head on 1973 340

Thanks for the reply. I got this car from a guy that was dying from cancer and has passed. He was a big numbers matching guy and I would like to stay away from aluminum heads, headers, and aftermarket intake. I'm committed to keeping the 8 1/4 in it.
Arthur wanted this car to be #'s matching and he was my friend. He got this car to within about 10-15% of completion and I'm going to finish it out.
The engine has been rebuilt or gone through. There's only a few receipts and it hasn't been fired up yet. I'm just thinking about the future. I would like to keep the 340 manifolds, have the heads ported and valves upgraded and find a LD340 intake to keep it in the stock-ish flavor. Also want to put 3.54 or 3.73 gears and a Tru Trac in the 8 1/4. I've always disliked rallye wheels but it came with 14's and I'll be upgrading to 15X7/8's. For Arthur.
Not the car I would build for myself but I'm just finishing it for a guy that wanted a car like it came from the factory. I want it to be like a car that Kowalski's speed shop got from the factory and hopped up. Stock appearing.
I would like to gain some insight on how I can get all the performance I can out of these heads while keeping the 340 manifolds and finding a Day 2 intake manifold (LD4B/LD340?).