There are plenty of "747 Combis" around, a number of operators have them although normally only a proportion of their 747 fleet.

Air India have three, their two 747-300s and one 747-400. Normal Air India 747s have a F12 C26 Y385 configuration (yes, only 10% of their seating is premium classes, that's their market), but the Combis are F16 C40 Y227, so only 283 seats instead of 423. There is a rear bulkhead and then a substantial main deck cargo compartment.

Boeing have made 747 Combis for many years, back to the old 747-200. Most people even riding in the aircraft would never notice. It's a substantial structural difference to the mainstream aircraft so normally only incorporated at time of manufacture - there have been just one or two post-modification conversions between the two types.

Different airlines have different approaches to the Combi. For example at KLM the majority of their fleet are of this type. British Airways, operating 747s to pretty much the same places, have none. Similarly, in Korea, Asiana have the majority of their 747 fleet of this type, while Korean Air with many parallel routes have none.