This list is DEAD! My question on 1956 Bus manuals was never answered.
Nobody knows. OK, I'll go to the next, a variation. What years cover the
1200-1500 engines? By any chance, would these be the years 1952 through 1965?
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the reason no one answered is because there is NO all encompassing book on
restoring your 56 bus.   or any other year for that matter,   so dont look
for it.  you will have to piece the info together.

your bus came with the 36hp motor, with the generator stand as part of the
case..  Not what is called the 40hp or 1200 withe the detachable generator
stand.   If you are happy going slow,:)  you can always crank it up if you
left the lights on :).

the buses started with the 25hp, until
1954 the 36hp, till
mid 59 the modified 40hp, a bad mistake, till
late 1960 the 40hp/1200. till
1966 the 1500   
1968 the 1600...........

I prefer my 1959 dealers shop manual to answer my 36hp questions.   I also
like Fix Your Volkswagen,  as the early editions have 25hp motors in the pics
 (like the 65 ed.)  This covers 36hp, but not as well as i'd like.   

the 63 edition (updated through 67) is reprinted by bentley or whoever, and
does not cover the 36hp motor.