one thing is for sure they are using a totally different kit
BC Stroker
GTM stroker
You can see the differences in the pistons, rods, and crank. Look at the skirts of the pistons, the rod journal through holes, and the big ends on the rods they are totally different. The GTM stroker is 96mm vs 88mm for BC, so a BC kit sleeved is 4.15 where as the GTM stroker is 4.2 Unsleeved. Sleeved engines are harder on head gaskets so if its a DD it is usually better to go unsleeved, if its an all out racer then sleeve it.