The Promax block is a BLP, which you can buy in DIY kit form from BLP with either the high or low IFR location for about half what Promax wants. You do need to be able to drill all the replaceable jets as part of the assembly process.
Do you use the vacuum port the original metering block has? Neither the BLP or Quick Fuel/ Proform "race" metering blocks have that feature.
There is nothing "wrong" with the original cast metering block, other than lack of adjustable tuning circuits. What is it you think needs to be changed?
