I'm not sure why you aren't running both Rest in Peace and Leyline of the Void, if your combo is based around the interaction with Helm of the Leyline. 8/4 pieces for assembling the combo is more consistent than 4/4, and it gives you some serious gravehate against the majority of the format. I mean seriously, I can't think of very many decks these days that don't use their graveyard in at least some way.

Although I suppose if you're going alot heavier on the Board Control plan and plan to play the long and grindy game until you assemble you're combo, you might not need as many combo pieces. My only concern at that point would be: why not just play a better Control deck (Miracles) that has two different I-Win cards that don't actually need to combo together to win (Entreat and Jace)?

Also, mana acceleration is pretty mandatory for this combo to even be worth it. At least with an opening Leyline, you're looking at a 2 card 4 mana combo. With RIP, you become a 2 card 6 mana combo. Mox Diamond + Land Tax could be interesting, but the Sol Lands work too.