Re-Introducing my 8month old rats :(

Hi! Posted here a couple times before, im trying hard to get my two rats, Jasper and Gus Gus back together again. I had to separate them a couple months ago because they were aggressively fighting non stop. I got Jasper (the aggressor) neutered, he still tries to bite me so i’m hesitant to handle him but i’m working on our bond. So regarding the introductions, i’ve been trying to figure out the best way to go about it, since they are so so so aggressive towards each other (prior to me getting them when they were 6months old I was told they got along perfectly fine together). I put their cages next to each other today to try to start getting them used to seeing each other. Upon doing so they both got EXTREMELY puffed up and started hissing at each other (it is still practically non stop). I’m wondering if I need to also get my other rat Gus Gus neutered to help this or if I should just stick it out and leave their cages next to each other until they learn to calm down. I don’t want them to be overly stressed and upset all the time though