The objective for the project originally was a simple one: try to make a running engine out of the parts that were gathered. With only 3 original heads, making just 1 fourth head (one engine uses 4 individual heads) seemed extremely hard. Furthermore, out of the 3 heads, one seemed an even earlier (test) casting with smaller ports and bore and the other two were doubtfull if they were useable for assembly.

So, the decision was made to make 4 new heads, designed from the old originals.
After studying the original castings, we were not convinced by some design solutions, so we made quit some smaller and bigger modifications, but still fully keep the main original design characteristics of the original Apfelbecks heads.
Most noticeable is the lay-out of the rocker shaft with the shaft protruding through the sides of the head (like the Scat split-port head design) for support. This seemed leak-prone to us, so the redesign now has the rocker shaft fully enclosed inside the rocker box.
For another more visible upgrade we took inspiration from one of the latest Porsche aircooled heads: the 993 exhaust port design, which aids in cooling and sealing. The exhaust flange even uses a stock Porsche 993 exhaust sealing ring.
BTW, the rocker shaft mounting also uses another original Porsche part: the 9mm locating pins.

With regard to cooling we used all original cooling fins to the full extent and kept a decent (big enough) room between the (tapered) fins to help cooling even more. This design with a little wider spaces between them also helps in the casting process.

Besides looking at the later Porsche aircooled design, we also tried to make the heads fit the type 4 case with as little modifications to an original type 4 case as possible.
Another design objective was to be able to use as many stock type 4 or OEM parts as possible. With that we had in mind that if we were to make a small series of heads, it would be possible for others to keep costs as reasonable as possible and make assembly as easy as possible. Not that such a complete OHC conversion is anything but easy or cheap though..

As of this moment, the case itself does not need to be machined in any way for mounting the OHC cylinder heads! The only case modification is drilling (and tapping) 4 holes, lower in the sump then the original oil return holes, because the lowest point of the heads is just a little below the original oil return openings.
Besides the above, you can use the original VW type 4 head studs for the Apfelbeck heads. You will however only need the shorter (top) ones, also for the bottom row. In other words, to mount the heads, 16 short (upper row) VW type 4 head studs are needed. This will work for most crankshaft strokes.
The benefits of 4 equal length head studs per cylinder (as opposed to the original 2 lower long studs and 2 shorter top studs) are evident: less chance for unequal clamping of the heads and therefore less chance of head-cylinder leakage.

For induction choices I noticed that – where original type 4 heads are closer to IDF spacing – the intake spacing of the Apfelbeck design almost exactly mimics the IDA spacing! This made drawing an intake manifold very straight forwards, literally!

In further pursue of simplicity and with what we as an aircooled community are familiar with in mind, the first billet intake manifolds now have a IDA bolt pattern, so the widely used and available Weber 48IDA carburetor would fit outright. Of course for optimal performance the original 48IDA will probably limit output in most cases: In flowbench testing of one the first casted heads with 2x 36mm (and 5,5mm stem) intake valves, we measured just over 300 cuft/min at 28” through the intakes with a 48mm IDA throttle body and just a 45mm internal manifold port. This was basically ‘as cast’ on a 98mm bore, so even further improvements should be possible, both from a little larger intake port opening as from using larger bores.