This should help you decipher what sort of engine you have in your Volkswagen. The "Code" column shows the first character or two of the engine code, stamped on the case. I supplied data for Porsche 914 cases as well as VW 411/412 cases just in case your Bus has one of those engines in it (since they are easily interchangeable).
Volkswagen Type 1
Code: Year: Engine:
4 1960 1200
5 1961 1200
6 1962 1200
7 1963 1200
8 1964 1200
9 1965 1200
FO 1966 1300
HO/TO 1967 1500
H5 1968-1969 1500
B6 1970 1600 (dual relief, single-port)
AE 1971-1972 1600 (dual-port)
AH 1973-1974 1600 (8mm head studs w/ case savers)
AJ 1975-1979 1600 (fuel-injected)
Volkswagen Type 2
Code: Year: Engine:
Numerals 1961-1963 1200 (see Type 1 listings)
O 1964 1500 (no cam bearings)
H 1965 1500
HO 1966-1967 1500 (no crossmember holes)
B5 1968-1969 1600 (single relief)
AE 1971 1600 (with crossmember holes)
CB 1972-1973 1700 (dual carb, manual trans)
CD 1973 1700 (dual carb, auto trans)
AW 1973-1974 1800 (dual carb)
AW 1975 1800 (fuel-injected)
ED 1975 2000
GD 1976-1979 2000 ('79 has Vanagon heads)
GE 1979 2000 (California only, Vanagon heads)
CV 1980-1983 2000 (Vanagon -- unique case and heads)
Volkswagen Type 3
Code: Year: Engine:
O 1963-1965 1500 (no cam bearings)
TO 1966-1967 1500
UO 1968-1969 1600 (fuel-injected)
UO 1970 1600 (dual-relief)
U5 1971-1973 1600 (7.7:1 compression)
X 1972 1600 (7.3:1 compression)
Volkswagen Type 4
Code: Year: Engine:
W 1971 1700
EA 1972-1974 1700
EB 1973 1700 (California only)
EC 1974 1700
Porsche 914
Code: Year: Engine:
W 1970-1971 1700 (8.2:1 compression, D-Jetronic)
EA 1972-1973 1700
EB 1973 1700 (7.3:1 compression)
EC 1974 1800 (CA-only, 7.3:1 comp, L-Jetronic)
AN 1800 (8.6:1 comp, D-Jetronic)
GA 1973-1974 2000 (7.6:1 comp, 3 intake studs)
GB 2000 (8.0:1 comp)
VO 1700 (Euro-only, magnesium)
1800 (Euro-only, magnesium)
2000 (Euro-only, magnesium)
Replacement Cases
(Never supplied in new cars -- only sold over the counter. All are
dual-relief with 10mm oil passages).
Code: Year: Engine:
F1 1300/1600
F2 1300/1600
DO 40-hp part if last digit is "X"
D1 Sometimes a 40-hp part
AB 1966-1979 1600
AD 1600
AK 1967-1974 1500/1600
AM 1600
AS Sometimes listed as Super Beetle orig. case
for '73-on.