Whilst the idea of having a 'shaped' combustion area may be sound and even be seductive the reality is very simple. You need a cut out for each valve to easily clear with the cams you are using. The nearer you get to 102 the deeper the recesses. This of course lowers the comp ratio. To increase it you need 'eyebrows' that is everywhere except the cut outs needs to go full deck height, even higher to take advantage of the gasket thickness. You need then a blended recess by the plug, offset as is the plug. so you are actually left with very little to play about with in order to get the desired compression ration. Yes you will likely end up with the 3 circle recesses, pistons will be handed too. SO the piston crown design is very nearly self sorting! What is not is the rest of the piston. The increased stroke will place the wrist pin higher, the cut outs if for larger valves may go right to the edge. The rings will therefore need to be lower to stop the top land being too thin and colapsing. Whilst you clearly need to allow sufficient material on the top of the piston to have and adequate thickness remaining once the machining is completed you must also retain sufficient clearance for the rods little end. It can get quite tight there if retaining the std Jag/Chevy .927 wrist pin. The next thing is that the High pin and low rings tend to interferre with each other. The wrist pin hole will likely be through the lower oil control grove. It may be recommended that this is sorted by using shaped buttons with the missing part of the grove machined in them, make sure that these buttons are hollow. Its known for solid versions to trap oil inside the writ pin and throw the engine totally out of balance.
My advice would be to get, beg steal or borrow a TWR piston of the stroke you are using and get it copied. They spent a lot of money getting this as right as they could and you wont beat them on your budget. I could sell you some Gp 44 6.5L pistons, they are not as refined as the Cosworth TWR ones but that may not matter dependant on usage. They also dont come with the heafty Cosworth price and 16 week lead in time.

 

I got the diagram from rob beere which is the same design as the twr pistons. valve reliefed for 44mm valve with a .05 quench height, and an offset dish. the pin height is something like 39.75mm, and used gm 96 mm rings. I got them reenginered by ross pistons

 

They are similar but not the same. Ask Chessman who are welding up one of my heads atm. You will need a mock build with plastercine or the like if you are using wild / high lift cams. I ended up having to cut the valve reliefs deeper and dropping a cam size because I couldnt cut as deep as I wanted/needed to and retain top land depth.

 

my cams are only 278 .440 lift, they aren't as aggressive as most of the race cams available. do you have pictures of your group 44 or twr heads?

 

That's just a tad more than my Cranes, which are 270 and .43

 

where did you get your over sized shims?

 

Shims are out 5/16 lash caps are in. Crane might do them. With titanium valves, better springs titanium retainer and lightweitht buckets you can rise the rev ceiling to a survivable 10K.
If you dont lighten things up the valves can bounce and smack the pistons with bad results.

 

where do you get these lash caps?

 

Got mine from Group 44 (Lanky RIP) but available at lots of places; in the UK this guy does them Wide Angle Top End | Denis Welch Motorsport
but try a cam manufacturere as they are standard (ish)