Hi Josh,

The late hydraulic head is not compatible with the open deck of the AL block - gaps are left open. I posted pics here many years back that showed the issue. I believe that the peanut-plug heads that do not have access to the lifters will work - just not the later iterations with access.

Cheers - M

A busy couple of weeks in progress, work, home and racing... all "stacked" together.

Thanks for posting this, it seems to confirm what I suspected but honestly, have never 'mocked-up'.

Basically, the 81 and newer "wide valve cover" hydraulic lifter head will not seal the open deck of an aluminum block because the large (1 inch diameter) pushrod holes (lifter removal access holes) over-lap with the alm. block lifter gallery dividing wall.

I have tried 77 to 80 "small plug" heads and they do not have this issue seeing that the pushrod hole - thru holes in the head are smaller. So yes, you can use a "peanut plug" head, but not the 81 and up "wide valve cover" version.

As already noted, no matter what head you plan to use on an Alm. block SL6, you need to fit check the head to the empty cylinder block, to be sure that the combustion chambers are centered over the cylinders.
Also be sure there is not a lot of valve relief on the sides of the combustion chambers, these reliefs help air flow but tends to undermine the narrow head gasket sealing surface, at the tops of the alm block's bores.
DD