I'd suggest doing a little grinding and/or filing on the front surface of the block and adding spacer shims between the pump and the block to prevent any distortion of the pump body while installing it. Hardened steel "Grade 8" flat washers are available in several diameters and thicknesses on Ebay, but you should be sure the block is flat before using them as spacers.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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