Because i'm crazy lol, j/k, honestly at the time i had no job and i had blown up my b16b engine, i had to get the car running with minimal cost but it still be somewhat reliable and fast which is normally not possible (cheap reliable and fast.). A good friend of mine gave me his blown b16a block for free, i ran the b18a/b pistons to lower the compression to what i wanted since the block needed new pistons anyway, my b16b head was still in great shape so all the parts went together and that was it
But there was a method to the madness, and i did have more technical reasons. The b16b head is better for a few reasons: The larger cams it has, the dual valve springs and minor port job. I chose the b16a block because I wanted to keep the 77.4mm stroke to keep piston side loading at high rpm to a minimum and have lower piston speeds since i was not using forged pistons and i have stock sleeves.
So yeah, it all came together for a few reasons, i had a theory, i had a budget and i was able to build what i wanted the best i could at the time.
Yes, just run a thicker headgasket to be safe and ARP head studs + good tuning and support mods.
As far as beating skylines it depends on which skyline and what mods it has, i'm sure you realize that.