What drive train makes the most sense for my build, a 1968 Coronet?

[66Satellite47]

Really good point. You need to be able to stop. My 10" drums on my '65 Coronet worked fine at the drag strip. Not sure they would have been really adequate on the street. The big 11x3 combination would be good.

 

[Budnicks]

Easiest may be a basic 440, if you don't know them well

a 383/3.75" stroke 4.25" bore 426 std., 431 0.030" over, 437 0.060" over
{cheap} pistons are readily available

or 400/3.75" stroke 4.34"bore 443 std., 451 0.030" over, 456 0.060" over
{either 383/400 with a 440 crankshaft} parts are easy to get
lighter crank, pistons & rods always helps, quick revving
lower/shorter deck block, more hood clearance,
narrower block more header clearance,

400 blocks are the strongest of any BB Mopar's Wedge Blocks
especially of the Low-Decks B-series

Good rods & piston is about the same cost for any of them,
or go a stroker 3.95" 0.200 offset ground {BBC size rod} 440 crank

if you go that route, a 440 crank in a Low-deck B-block
the mains need to be turned down to B spec.'s
the counter weights need cut down to be appr. 7.125" diameter
lighter crank easier to balance too, rev's great...

You can get them done already, several sites, Mancini Racing or 440source

A RB 440 is more expensive "usually" initially to purchase,
there are deals sometimes...
440 about triple/quadruple the cost of most 383's, 100's of thousands made
440 probably at a min. double/triple what a smoger 400 is
all the rest of parts are about the exact same costs, as a 440
IMO it'd be a wash money wise...
Depends on your preferences, availability of parts you need/want...

Good flowing heads are a must for any of the above...
Whether it's just a street-beast/street-strip or just a cruiser,
Be it alum. or iron, larger valves & better ports, better flow,
because that's the biggest choke point really
that impedes making any real power in a BB Mopar, is the heads...

The rest is basically performance 101 stuff, to get 425hp+ out of a BB

Good luck

 

[66Satellite47]

Not sure about cost difference between 400/383 & 440. Comments on heads are sure right on point. You can grind a lot out of stock iron heads & make pretty good power but new aluminum heads probably make more sense.