hopefully when you pulled the lifters out you kept them in order so you can put them in the same place they came out of. the lifter mates to the cam lobe.
I've had hydraulic lifters that wouldn't keep preload because they were bad. sometimes they just keep collapsing.
if I were you I'd get some new lifters at minimum. like others have said, there is a lot of info on setting up your valve train online. If you got a IM gasket set with the rubber things, throw them out and use an appropriate sealant instead. again, there are a lot of videos on sealing up a sbc IM.
good luck