Adding std SB heads (oil trhu deck) to a Magnum block.

You're better off just going with new oil thru pushrods and oiling the top end that way. Just be sure your lifters have the oil hole on top. That Magnum block/LA top end oiling is a very difficult deal to get done. The passage must be exactly placed and it's like 6" long. If they are off even 2-3° in any direction you will not line up with the cam bearing hole.

I should add this is how a lot of high rpm race engines are done because it lets more oil be diverted to the lower end.