The intake has to match the heads, not the block, so if you have Trick flow heads and an LA pattern intake those match and can be used on a Magnum block.
Double check your rocker arm part numbers. If they have the oil through pushrods provision they can be used with your Trick Flow heads on a Magnum block. If they were LA style without the oil through pushrod provisions you need different rocker arms.
You can run the factory Magnum hydraulic roller lifters with a new hydraulic roller camshaft for either LA or Magnum.
I do not know if the LA retrofit hydraulic roller lifters will fit a Magnum block because I never tried it yet. The top of the lifter bores on a Magnum block are a little taller than an LA block.