From a recent post that was made by "200dragstang", might be a few answers to your question. Good luck
66 water pump 3-15/16" late model about 7/8" longer.
Front to back
Water pump to crank flange 30-3/8'
Block 26-3/8'
Water pump to flywheel 31-9/16 You will have to add what ever you add to the pump flange , pulley, spacer, fan, bolts .I do not have those together but could find if you need.
Best as I could do with a tape. No responsibly will be taken for these measurements!!!!