I'd personally take the 68 year model Coronet ?
{I assume from what you wrote, 68 it's not a Super Bee ?}
over a 70, 68 is my favorite year across the board,
But if ones a Coronet & not a Super Bee ?...
That may sway it towards the Super Bee for me...
Unless the 68 is an R/T, hands down then the 68, regardless of trans type...
I like the 70 V code Super Bee 440 six pack 4 speed & Dana 60, I really like that combo,
not a big fan of red though, I do think the 70's body style is a good looking car...
But the 68 I like better, so it would be a tough choice...
Really depends on what all came, with what car...
But best of both worlds is a 68 Coronet 426 Hemi 4 speed {18 spline} & Dana 60 would be cool as hell,
but that's not an option, so the Hemi & 727 Auto would be cool too...
Buy both...LOL
But for the best bang for the buck, which is more complete ?,
is one more complet more trim & hard to find parts etc. ?
does either one have any of the OE engine or drivetrain ?
does the 70 have 440 six pack manifold & carbs or engine &
the 18 spline 833 trans or Dana 60 still ?
The 68 with no Hemi, no K member suspension or drivetrain in the 68 ?
IMHFO your just basically buying a fender-tag, vin & build sheet
unless it's a screaming deal I'd pass, it will cost 2 times as much to build correctly...
NOW
If $$$ isn't a factor, the 68 Hemi car can bring more $$$,
I guess if your not going to sell, building it for yourself, it doesn't really matter,
But if you can find & use the proper date coded parts
& it's done correctly, the Hemi car can theoretically bring or be worth more $$$...
If it's just for fun, seat of the pants, shits & giggles buy the 70 Super Bee
440 six pack 4 speed car...
If it's for bragging rights get the 68 Hemi car...