I constructed this out of 2 pieces of galvanized pipe. 3/8 x 2 inch and 1/4 x 2 inch pieces. I sanded down the 1/4 inch pipe to fit inside the 3/8 inch pipe, got mine about half way or better.
The bushing fits pretty good in the holes in the deck, centering the guide on the broken bolt. I used a left hand 1/4 inch drill bit from autozone. After some time the drill bit caught enough to back the bolt out. If the bolt doesn't back out you will be able to use a bolt extractor to remove it.
I learned this the hard way as I damaged my block slightly before I constructed the guide. This is the result before my thought to construct the guide bushing
Construct the bushing and save yourself the added aggravation of damaging your block. Also remember to use PB Blaster and let it soak to help loosen the threads up.