Quoted article from WOT-Tech:

"Taking the stock 3400 for an example, we have a piston that has a flat area around the outside, and a heart shaped combustion chamber on the head with lots of flat area around the outside. This is a great design to put the mixture into the center of the cylinder. The stock piston sticks out of the block .020" and the head gasket is .060" thick. This leave .040" between the top of the piston and the surface of the head. .035-.045 is considered optimal quench distance, depending on the RPM you intend to run. For 5000 RPM on stock forged connecting rods, .035" is enough space. For 6000-7000, .040" is enough. Past that and .045" should be used. The reason being that connecting rods stretch at higher RPM. You must account for the stretch or there will be a greater possibility for piston to head contact.
For custom pistons, the piston height can be adjusted easily and either the gasket or head can be changed from a stock spec to give the beste quench. For stock engines, the following should help you choose your MLS gasket thickness
3100 - Piston sticks out .020". Head Gasket should be .060" thick (Stock)
3400 - Piston sticks out .020". Head Gasket should be .060" thick (Stock)
3500 - Piston sticks out .010". Head Gasket should be .050" thick (Stock is .060")
3.4 Iron Head - Piston sits .010" below deck. Head Gasket should be .030" thick. Compression will be increased but no problem on iron heads. Compression will be in the 13:1 range using 3400 heads."


Based on this article quoted from WOT-Tech, I'm guessing our pistons sit .010" below deck like the 3.4 RWD? or are they flush? I know they don't pop out, just not sure if they sit a little below or not, and by how much if so.



Also if anyone can tell me how far the valves open on a 3400 or 3100 late model head I could use that info, as I'm wondering if I'm going to encounter an issue with too much lift and have pistons hitting valves...I noticed the valves are not nearly as recessed as they are on the iron heads.

 

I've read that you may encounter problems with the valves using 3500 heads. Yes, the pistons on our 2.8s and 3.1s, according to 60DegreeV6.com, come to TDC about .0165 below the deck surface. Keep in mind also that the valves on the late models are also slightly bigger (1.78" intake vs 1.76 iron head).

Also, you will need to swap pistons with the donor engine. The flat-tops won't work. 3.1 pistons would be a good choice for mid-range CR, though.