Ah, now I see what you mean...firewall clearance
There are two MSD distributors for the Cleveland, a large cap and small cap. You need the small cap version to prevent the distributor hitting the firewall and destroying the cap as soon as the engine is under load.
It sounds like the 8577 is the large cap version or maybe it comes in 'large cap' & 'small cap'? I think the one I purchased was the 8477, mechanical & vacuum advance, (but you could remove the vacuum if you want to stay with mechanical only).
Julian
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