Thanks67 and down heads had a less efficient chamber design, 60-62 heads had looser control of the chamber placement in the casting except for the "special" or star casting mark heads intended for the aluminum block motors.
All 63 and newer heads have the tighter chamber placement tolerances and will work on aluminum or iron block.
All 68 and newer heads have the same chamber.
Drool tube heads are a little lighter than the late style heads but are functionally identical.
This.Here is a little background and history on the Aluminum Block Slant Six engine
You can read about it here. The aluminum block has freestanding cylinders and an open deck. It has a very narrow cylinder sealing surface and a special head gasket. The chambers have to be aligned perfectly over every cylinder bore for proper sealing!
If the top of the cyl could be built up, welded without warping the **** out of it...it would cure the weeping issue most have around 60-70k miles.I'm working on an aluminum motor also, mine has plenty if sediment in the bottom of the water jackets but the tops of the cylinders are nice. I haven't gotten into it far enough to determine if it's rebuildable or not but so far it's promising...
Doctor Doug omitted the "squirters" altogether on "Twiggy." Used some aftermarket rods IIRC for a non-/6 application. Funny thing about bearings is - no oil out = no oil in! I predicted the end result as I was reading the thread and was unsurprised when poor Twiggy tossed a rod through the block in protest on the freeway...
The aluminum blocks don't take kindly to welding from what I've read. I know one of DD's aluminum builds had a welded closed deck and massive warpage issues. Another had the top deck closed with hard block. Both engines were short lived after the good Doctor's "treatments."
Money shot:Here is a little background and history on the Aluminum Block Slant Six engine
You can read about it here. The aluminum block has freestanding cylinders and an open deck. It has a very narrow cylinder sealing surface and a special head gasket. The chambers have to be aligned perfectly over every cylinder bore for proper sealing!