What's the big deal about Horsepower?
If you're doing a big bore L28, your going to need an N42 block and be sure to have it Sonic tested to be sure the bores are thick enough after the 3.0mm over bore. The common thought is to use the siamesed F54 block, but I will be very surprised to see any F54 block capable of taking an 89.0mm bore and the N42 block has a higher silicone content.
This L31 engine has been done to bits and very well documented online, but turbo is not normally the way to go, because the bore becomes a bit thin and under high boost pressure, the bores are porous.
I'm doing an 87.0mm bore (2818cc) 380 injectors, about 250HP @ wheels and over 600Nm torque, so who needs HP.
Your going to need; LD28 diesel crank, L24E rods, KA24E pistons for your bottom end. Rods should be chromoly or H beam forged & pistons forged to KA24E specs.
Cheers, D