Really no need to place the o2 sensor that far back IMHO.
Best spot is right after exhaust collector, where it is closer to engine.
Farther back will add a delay to reading, it'll work after the "y", but there is really no benefit to speak of.
Far as a fuel pump, there are plenty that will supply enough fuel.
Guess-timate your HP, and select one.
For example a generic e2000 is probably good for ~250-300hp.
Pump doesn't have a psi rating, the regulator does that.