offenhouser or a airgap?

The RPM (Air gap or not) is super hard to beat and most likely the best deal for a street car hands down. If your looking to make a good effort street striper, same description as above except sometimes a single plane is what you want over a dual plane. Offenhauser makes a intake called the "Port-o-sonic" that needs a minor mod to it, but is an real good intake. IF you allready have that one and are doing a agressive engine, i'd stay with that.
Otherwise, I'd do a RPM.

Roll Master, a timing chain from down under is one of they absoulte best, but they will even strech after some time. Mopar makes a niffty little item called a timing chain tensioner and they can be purchased brand new from the dealer or Jegs/summit racing. There under $40 and keep tension on the chain so it doesn't bounce around. The chain will still strech, but not act sloppy in the case.