Hello, Yes you can also apply for both the exams. Even If you are eligible for SBI SO you can also fill the same form. Acandidate can fill both the forms PO and SO in same year whever the vacancy out.

The best books for the preparation of this exam are as under:

Data Interpretation By Arun Sharma

Quantitative Aptitude For Competitive Exams By R S Aggarwal

Lucent General Knowledge

Banking Awareness By Arihant Publication

hope this will helps you