To see the differences in the Type 1 and Type 4 cases, we need to look at both and analyze them.
The Type 1 crankcase in the photos below is a 1600cc (1.6L) "B" case with the dual relief oil system. It is relatively stock with the only changes is that it was bored for 92mm cylinders, welded flywheel area behind the #3 cylinder and had a sand seal installed. It features 10mm head studs, and 8mm oil pump studs.
The Type 4 crankcase pictured at the bottom is an AW series Type 4 from a 1974 Transporter (U.S. model) and was originally an 1800cc (1.8L). This case is also basically a stock case, but a couple of modifications have been done. One of the oil galleys has been drilled and tapped to run an external oil filter and/or external oil cooler. The other modification was the long dipstick tube, seen in the photo coming out next to the breather tower.
From the front you can see many similarities. This Type 1 case displays the mounting studs for the generator/alternator stand, studs for the mechanical fuel pump, and the oil pressure switch can be seen to the left. The distributor is mounted between the oil pressure switch and the fuel pump. This case has been cut for a sand seal so the case material around the pulley area is thin. The crankcase identification number can be seen directly below the mounting studs for the stand and the oil level dipstick is visible to the right.
Front the front of the case there are many points of interest to make note of. The first point is the oil filler flange on the bottom right hand side of the photo. It's a two-bolt flange molded into the case. In this photo, on the left hand side are the three mounting studs for the oil cooler, seen right below the distributor. Right below that are two oil galleys. They are plugs for the galleys that supply oil to the oil filter (a real kind, not just a simple screen). The oil pump operates on the same principle at the Type 1: the camshaft turns one of the gears in the oil pump which spins another and that forces the oil through the oil galleys.
Looking at the bottom of the oil sumps, differences are apparent. The Type 1 case only uses a 6 bolt plate to bolt the oil strainer. This plate also houses the drain plug. The only other items of note on the bottom of this case are the oil relief plugs, with one being quite visible in this photo. This plug looks like a huge slotted bolt head located on the top left of this photo. The other feature is the finned surface of the oil sump. There are two reasons for this: ribbing provides for a substantial increase in strength and a minuscule amount of oil cooling, though the change in temperature is unnoticeable.
On a Type 4, the drain plug is separate from the oil strainer. There is also a second plate on the bottom of the Type 4 case, though there is much speculation about it's presence and use. A long time VW enthusiast told me that it was used for a dry oil sump application in industrial applications. At this moment in time I have no confirmation of this.