18,000 orig. mile 318 build

Well guys the car has been tucked away in my garage do to weather. Since my last post I did come across and bought a B Body 8.75 rear. I got it cheap enough but need a lower gear ring n pinion and think im going with a spool. So far im debating on buildin on the current 318 or drop in my 400 from my now retired pulling truck. As of now looking for opinions and weighing out cost of both. Reason I was thinking 400 because thers alot of goodies already on it. MSD pro billit dizzy, Mopar M1 single plane, KB pistons, Ported with bigger valve 906 heads, Lunati .525 lift solid cam with crane roller adj. rockers, ARP rod n main bolts, cloyes double roller, HV oil pump etc.... Opinions??