I agree of course that both Gonzalez and Rosewall would have won several Wimbledon titles.
It's a more delicate question if Pancho would have won a French Open title. On one hand clay was his weakest surface, on the other hand he reached SFs of Roland Garros in 1949 and 1968 (when he was 40) and had some fine clay wins as a pro. He beat Cooper, Trabert and Sedgman in the 1959 Toronto tournament, he had wins against Laver on clay at Knokke in 1964 and in Hollywood, Florida, in 1966.
In the 1950s Pancho would have tough opponents on clay: Segura, Rosewall,Trabert, Hoad, Sven Davidson, Drobny, Patty, Cooper, Ayala and in the 1960s Rosewall, Segura, Hoad, Cooper, Ayala, Pietrangeli, Santana, Emerson...
I speculate that Gonzalez would have won at least one French title.