360 magnum budget build

So how much of a cam can the magnum heads take without changing valve springs and retainers? I played a little bit with comp cams Camquest software and the best power I got with a nice flat torque curve was with their 20-604-9 cam (210-220@0.050, .512 lift on a 112 lsa)

They also have 20-624-9, same specs but with .480 lift.

Comp says those 2 cams can't use stock springs...

I don't really want to start investing in the stock heads. If I have to change springs and retainers, I might as well go straight with the EQ 2.02 magnum heads.