(1) If the #62 heads have 1-piece stainless valves & hardened seats, and are ready to bolt on, then the dished piston route is probably better.
(2) But, if the #62 heads are not as I described then, IMO, the 6x-4 heads & flat pistons are the better way to go.
--(A) The Speed-Pro L2359NF forged pistons, are still only a little over $300. Dish pistons are twice that. Some buy the SP pistons & have a dish machined into the piston tops. They're plenty thick for that. Many have done it. Some say a D-shaped dish is best. That will cost more, since most machine shops can easily cut a round dish, but not a D-shaped dish.
--(C) Some like the Icon pistons, which are made of the 2618 material, same as racing pistons. These require more piston to cyl wall clearance, since they expand more. These come in both flat top & dished.
--(D) I recommend Auto Tec pistons, BECAUSE they are made of the 4032 material, & can be ordered with the pin location of your choice. This allows you to order the pin height you need, to achieve near zero deck height, WITHOUT having to have extra material removed from the block deck. The machine shop will just do the needed square-up deck machining, then measure to see what piston pin height is needed to put the piston top even with the deck, @ TDC, & you or the shop can order the pistons. From everything I've read, Auto Tec will not charge extra to put the pin hole where you want it. Yes, Auto Tec pistons cost more than Speed Pro. BUT, you save the cost of the extra machining, in order to achieve zero deck height. Always better to machine away only the material that must be removed to square the deck up with the crank centerline.
When I called Auto Tec, they told me I could buy pistons cheaper from one of their hi volume dealers. They recommended Shannon's Engineering. He claims that he'll beat anybody's price on Auto Tec pistons.
(3) You mentioned going with bigger valves in the 6X heads. No need to do that ! They work just fine, unless you plan to have the heads fully ported, for max flow & power. There are 2 reasons you don't need to do it.
--(A) Valve seats in the 6X heads were factory hardened for use with unleaded gas. Many have posted that when you cut the exhaust seats for the larger 1.77 valves, you cut down passed the hardened metal, meaning that if you wanna keep hardened seats, you'll have to pay to have hardened seats installed. That's extra cost. Some say the hardened seats are not needed, & they've been running without 'em for 30 years or more, without any problems. Others say they've seen sunken valves because of soft seats. So, take your pick.
--(B) Many have probably gone with 1.77 valves because the very popular Ferrea brand 5000 series valves do not come in a 1.66 size in the correct length. Butler machines some of the 1.77 valves down to 1.66, then sells 'em for about double the price. So, most just go with 1.77's.
But, SI valves sells 1.66 valves. Part number is 6001SG. One of their salesman even told me that their cheaper replacement 1.66 exhaust valves are 1-piece stainless, with the factory type 2-groove tips. The lower groove is for the factory type rubber O-ring seals. But, I think most everybody nowadays goes with 1-groove valves & has positive valve stem seals installed.
Many say they have spent over $1000 having iron heads built correctly. But, the correctly built new alum heads are around $3000, with bolts & shipping charges. Some say the valves & springs that come in E-heads are of poor quality, so that you need to have a competent Pontiac head shop build the heads, starting with bare cores, then adding the good parts & doing the correct machine work. But when you say that, some will usually say they bought out-of-the-box E-heads & they are just fine. Again, take your pick.
PS: If you're actually building a 400 block stroker, rather than using a 455 block/crank, the stroker assembly can be ordered with whatever custom pistons you need.
