The bottom one almost looks too good to be true... perhaps like someone producing barrels has started to repro barrels with the correct number stub... but until anyone else could corroborate that, there is nothing that I know of to suggest it isn't genuine.
If it has the notches out of the top fin then look for the thread (here or s'erotica) that discusses SX/GP port specs.
If it does not have the notches then you'll need to take a tracing of the exhaust port to see if it is wide and shallow (early ring-breaker) or narrow and tall (knee jerk reaction to resolve the ring breakage issue).
The above presumes that they show no signs of tuning work to the cast post surface.
Adam
Very welcome
