Trf of tenancy rights

An individual wishes to transfer his tenancy rights in a residential property in favor of a builder. Tenancy rights is a capital asset and shall attract capital gains.

1) How does one arrive at a cost of acquisition to compute long term capital gains? Tenancy rights acquired before 1981.

2) Does one need to prepare a transfer deed duly stamped and registered or a mere MoU will be sufficient? Builder wants to make an MoU only.

3) Is section 54 and/or 54EC available exemption in this case?

Thanks