Yeah, I was seriously considering swapping to an LA aluminum timing cover until I found out that wouldn't work. Well, it would fit the motor OK, but the fan would end up in the wrong place, maybe even hit something.
FWIW, the new timing chain and the Mallory distributor are LA pieces that just dropped right in. LA fuel pumps OK, too, although I'm running a NOS 318 poly fuel pump - a rebuildable Carter that looks like today's Carter street/strip pump except for 5/16 inlet/outlet instead of 3/8.
And here is a 57 301 poly (which has a 318 bore, 277 stroke, i.e., 3.91 x 3.125):
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