the DG2813 IS "slowbeat" Asian21j. Most Asian 21j will have this movement or a variation of it. It is a 21,600bph movement.. and gets 4-5 ticks/second. The "highbeat" version is the DG4813.. which is the same movement modified to have a smoother sweep. It generally gets 6-8 ticks/second. Not many dealers include this version in their watches, but it is equally cheap and you can find the 4813 for around 35 dollars new and the 2813 for between 20 and 30usd new.
The swap depends on the canon pin. There are 2 versions.. one with a recessesed cannon pin(where the hands attach to the movement) and another version with a protruding canon pin. find out which version your watch has and buy the apropriate movemennt. They are both swapable with pretty much any watch that will be sold as "Asian 21j".