318 intakes - old style?
Blanket statement that's mostly true.... but, not in all cases. Small block Holley Street Dominator was a single plane that I did a comparison against other dual plane intakes such as Weiand Action Plus and factory cast 4bbl intake and the SD cut the same 60 ft times. Some stock engines came with single plane intakes that created lots of low end. Like the older 318 single plane, not shy on punch whatsoever.
LM318 Marine four barrel single plane, is the same casting number as 273 four barrel, but has a taller carb mount, which is then machined at an angle to match the installed angle on a boat, so carb sits level(parallel to waterline). Uses a Carter 4 barrel, forget tag number.
I owned a 1974 Century Ski Fury with one in it, one of 57 that year, and 206 over three year run, '73-4-5.
It seemed to take a while to dig out of the hole upon acceleration, but boat is a deep-vee and has more drag at low speeds.
It will go 44mph @4400rpm, which is handy, as old boat speedos suck for accuracy.
You can also 'regear' by changing either propeller pitch or slightly more cup for a smaller change. Of course, you're then going to lose top speed, and possibly speed holding for slalom skiing, as originally sold as tournament style ski boat.
So factory Diameter & pitch probably best.
That LM318 run of engines(don't know how many) were built during 1968 model year, IIRC so probably have same componants as car engines of that year. Then were warehoused until needed.
Some are opposite rotation so crankshaft can't be used on a car or rear main seal will leak, as wipers 'hashed' in wrong direction.