Applying B2 for two week Conference travel three months before joining job with approved I797B

[Birjoo]

Hello, I was on F1 in 2016 first half and had to leave to India last Feb due to family situation. It took an year to get the J1 waiver from previous J1 status in January 2017, and got a cap exempt H1B approved for a job which was actually supposed to start July 2016. Employer has asked to join July 2017 after the stamp at Mumbai consulate. But I will only be able to enter ten days before the start date. 

For the stamp etc I need my original certificates etc which are in storage, and I also need to travel as an aide to a prominent international leader in March to a conference in USA. I am not sure if I should apply for H1 and then visitor visa or apply for visitor visa-while telling them that I shall travel back to India to get the H1 stamp after the conference? Please advise.

I also have a F1 stamp valid till 2020 and can get an I20 in the previous program until June 2017. Not sure if that would invalidate the H1 or not. Although that would be the easiest thing to do, I feel there is a risk and would like to get advise. Thanks