Big ports have larger ports, more flow, but less velocity in ports. Normally 3 rib blocks, 9.4:1 compression ratio.
Small ports have smaller ports, more velocity in ports, normally make more power. Only came in FWD format. Normally 7 rib blocks with oil squirters, stronger block, 10.3:1 compression ratio.
Quick way of telling is to look at the intake manifold. If it has TVIS sticker on it, it's normally big port. If not, it's normally small port, but using this technique isn't accurate because the manifolds can be swapped over.
Best way is to just take a look at the intake ports, small ports are obviously smaller.