Just my first reaction, You should't use the other intakes as guides. Runners are larger, and plenum doesn't have those cast in bulges between pairs. So you have to look only at what you have for improvements.
I don't think you can remove the plenum reducers between the pairs of ports I think they are cast in, you could reduce them some. Thin up the dividers, and put a open spacer on it. If your 318 has 340-360 port heads on it that intake will never work. If it has 318 port size heads on it I really would't do much, I'd put a 1 or 2" spacer on it. and call it a day. Judging by the size of those runners I'd start my shift rpm about 4800. That's the main thing I'll say, imagine doing a full runner port/enlargement on every runner. Use the part as intended, for a nice little 2 bbl 318 upgrade.
Depends on what your intentions are.
Years ago I had a 79 power wagon with a 318 bone stock, I put an sp2p and a holley 390 cfm double pumper (one of the early circle track carbs). There was nice, noticeable improvement over the stock 2bbl set up.