Plumbing
in parallel will have lower pressure drop; and likely some advantage in heat
rejection because of higher average rejection temp.
Rotary engines have a high oil
flow. Twelve ft of -8 line and two coolers in series could have quite a
high pressure drop starting up on a cold morning. But once things are
warmed up, should be OK. Personally, I’d opt for at least -10 line.
FWIW,
Al