As far as I've ever read you can use any type cam and most lifters in an LA (jump in guys and correct me if I'm wrong)
or magnum block without modification. The pushrods are the tricky part. There have been guys post failures lately because of the wrong length pusrods. It depends on how much you want to dink around with a strange combination of cam, lifters and pushrods.I have the same thing going with my 318. It came with a roller cam but I'm putting in a flat tappet hydraulic. I haven't mocked it up yet but when I do I'll ckeck the pushrod length carefully so I don't wipe out a lobe or two when I start it up. I have all the correct parts to put Magnum heads on my LA block if I go that route.
The cam bearings are a babbit style and should work with any cam designed for your block. The oil holes in the #4 bearing come from the mains and go up through the block and heads to oil the rockers through the rocker shaft. From what I've seen and read about the hybred you own I would consider it a Magnum and build it accordingly. Good luck! Mike