can i use 2 13b's to make up 1 20b motor and what do i need

There are plenty work to be done . unless your pocket are lined with gold dont atemp, custom , balanced e shaft to be made up..custom oil and water lines, custom sump, custom intake, all to bemade from scratch. So have a trusted engineer to atempt that...custom headers or downpipes bigger radiator, at least 2 high powr feul pumps, plenty custom wiring and management. A few thing to think of....only a few..still plenty of other things that wil pop up...but all depeds on your choice of usage for the car..