Conversion from MAS to MAP on TPI. Help!

Guys.. i am new at this forum. What brought me here is that i need to convert my current TPI system. It is from a 1989 Camaro IROC-Z. It is MASS and i need to convert it to MAP.

i have researched but can not find the information on how to do this conversion. It seems to me like it is very easy. Has anyone done this before? I just need to be pointed in the right direction.

Thanks!
-Jorge