Need a plan - component selection for restoring 68 340 that runs on 91 oct

The piston type that wyrm is probably referring to is one that has a small raised quench pad on the edge above the eyebrows. This pad will poke well above the deck into the 'open' part of the stock chamber. (The 'open' part is the shallow flat area of the chamber opposite from the spark plug side.) This quench pad will come up veery close to the flat area at TDC and form a quench/squish area, and that effect will help fight detonation, while raising CR to help low/mid RPM torque...good torque is what you want on street driving/cruising.

The challenge in this with the stock type open heads is that:

• All of the pistons' height relative to the block deck have to be measured (that can REALLY vary), then the block milled to equalize all the piston deck heights.
• The open area's depths in the chambers vary some. That has to be measured on both heads, and them maybe heads milled to equalize those.
  
• Now the quench pad has to be milled down, in conjunction with selecting a head gasket thickness, to make the top of the pad come to about .035-.045" from the open area in the head, at piston TDC. You need get in that clearance range to make the quench/squish effect work well but not get too close and have piston contact with the heads over the long term or at very high RPM's.

So, you can see it is several steps of work, machining, and cost with careful measurements; that kind of work may be done commonly for more serious engines, but it is a lot of work for a rebuild that is meant for more 'casual' use.

This is all a lot easier to get to work with closed chamber heads (like the AL Edelbrocks or the cast iron Indy heads) with flat top pistons. You get rid of the problem of the depth of the open part of the chamber and all the rigamarole of adjusting that quench pad height. (And you get larger quench pad areas.)

IMHO, for making life easier for your goals, I think you are best off with the 2 flat top piston types mentioned. However, this is not 'best performance' in terms of:

• fighting any detonation tendencies with 91 octane; you will have to do that with tuning ignition timing as said
• best possible low/mid RPM torque

So it is a choice you need to think about what 'best performance' means to you in terms of expense and effort versus results.

BTW, for a KB quench dome look at PN 373, it is listed for 360's; you just buy a big enough oversize to fit your 340 bores...if they are not too large.