Why do you need to get the block decked? gt30 should work fine on a standard yb with grpA bolts and gaskit mate as long as it set up for it with the right injectors.
my brother was running a standard yb with grpA gaskits and had a t4 and light blues at 2 bar boost. he used it every day and i didnt think it was laggy. was a nice car to drive
just put one on and try it