Another way to go about it, if you aren’t up for buying any top end parts initially, and don’t like the prospect of potentially having to buy stuff more than once...... build the RB 505 and reuse your entire top end.
Then, if that doesn’t get you where you want to be....... replace the top end with something “bigger”, and sell off what you have.

If you do a low deck, you’ll have to buy an intake, then when you upgraded the heads, you’d have to buy another one.