June 23 (Reuters) - Mexicans Carlos Pena and Eduardo Herrera have signed three-year deals at Rangers, bringing to eight the number of players to join the Scottish side this summer as manager Pedro Caixinha overhauls a squad that finished 36 points behind champions Celtic. Financial details were not disclosed but reports in Mexico suggest Rangers paid a combined 4 million pounds ($5 million) to Guadalajara and Pumas for the pair. Portuguese manager Caixinha has already added countrymen Bruno Alves, Fabio Cardoso, Daniel Candeias and Dalcio to the squad, as well as Aberdeen captain Ryan Jack and Colombian youngster Alfredo Morelos. The club, who appointed Manchester City academy director Mark Allen as their director of football earlier this week, have also been linked with a move for Norwich City's Graham Dorrans. Rangers, the 54-times champions of Scotland, won promotion back to the top flight in 2016 after a four-year exile from the elite, which began after their financial meltdown and liquidation in 2012 when they were demoted to the basement of the Scottish game. They finished third behind Celtic and Aberdeen in a disappointing return to the top flight, where 56 goals in 38 games was just over half the tally recorded by the champions (106). Powerful forward Herrera said he was aware of the pressure he would be under playing in Glasgow. "I know there is a lot of pressure which comes with playing at a big club like this but I have also played with my national team and with big clubs in Mexico so I am prepared for the task," he told the Rangers website (rangers.co.uk). Rangers' season officially gets underway with a Europa League qualifier against Luxembourg outfit Progres Niedercorn on June 29 at Ibrox. ($1 = 0.7888 pounds) (Writing by Peter Rutherford; Editing by Frank Pingue)