Holley interchange parts.

Will a primary metering block from a 600 work on a 750,thoes blocks are kind of pricey.

It'll work, as in the car will start and run. It may not run the best.

Stock Holley metering blocks look pretty much the same. They can differ, though, in the diameters of the little holes that meter. For example, the Idle Feed Restriction and the Power Valve Channel Restrictions may be different sizes. There may be differences in the emulsion tubes. Most of these differences will be so small that you'll never know the difference unless you use precision pin gauges to check, and I don't believe the sizes are readily available in print.

Also, if you're going to spring for a new metering block, it may be wise to buy a billet block.

I'd be asking some of the carb experts out there for more specifics.

There should be quite a few on shelves of Board members who have replaced them with aftermarket blocks.

R.