As stated, you have to pocket the block.
This was recently discussed at length on another board where I post. Basil doesn't like us posting links to other boards so I'll have to paraphrase the comments here.
Those who had put a 1275 head on a small bore block generally complained about the performance of the car when they were done. They spent a lot of time trying different needles and some even resorted to removing the head and shaving some off some of the head to get the compression back up. No one who had done this (for a street motor) was happy with the results.