Motorcycle Repair: case boring for big(er) bore kits on harley sportster, harley sportster, domed pistons

Question
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Wisco has 3-13/16" flat top pistons and cylinders for sportsters. They state that this settup fits stock sportster 1200 heads. They also have another same size settup that fits thunderstorm heads. What would be the advantages or disadvantages of stock heads over t-storm heads? I would prefer to keep my torque high at the low end of the rpm range, which head would be better for that?
Thanks
Pat

Followup To
Question -
The bike: 1997 sportster 883 converted to 1200cc in 1999. It has dished S&S pistons and the original 883 heads with little head work performed.
Is it possible to bore the crankcase cylinder holes large enough to install cylinders with 3.75 inch inside diameters? Wiseco says the holes should equal 4.005 inch.
Presently, the cylinder holes are approx 3.625 inch
Thank you
Answer -
You can bore out the stock cases to 4.010" to accept AXTELL 3.13/16 30 degree domed pistons and Cylinders and use your stock stroke and have a 88 cubic inch motor or 1450cc motor. You will have a square motor which is great for hi rpm's. I run one of theses with STD heads and make 145 horse power at the rear wheel on the dyno.  Johnny

Answer
The Head bolt Pattern for 883 and 1200 and 89" and 88"  all use the same Case stud bolt Pattern, So any sportster head will work. As faw as cylinders goes, You have to have the cases bored to go any bigger then 3.1/2" bore.  so 3.5/8" and 3.13/16" cylinders will NOT fit the cases unless the cases are bored. Use your stock heads for the torque you want.  Johnny