1984 corolla SR5 SOHC to DOHC conversion

I maybe purchasing a 1984 Corolla SR5 HB, but wanted to know this before i make up my mind so any help would be much appreciated. I know that the 84 SR5 is SOHC(well most SR5 are SOHC as far i know, which ain't much mind you), but I was thinking of doing either an engine swap for an 4AGE or is there a way to convert it from SOHC to DOHC and if so how much would it cost for 1) 4AGE engine swap 2) to convert to DOHC.