914 engine swap

Yes it will, but the engine tin, exhaust, and F.I. system are very different. Your oil fill and dip stick housing will have to be removed from a van engine. You will have to modify the 914 engine to accept the parts. Its been done but to do it correctly its very time consuming and costly. A van motor can be had for much less money than a 914 engine

914 has a 215 mm flywheel and bus uses a 210 mm. 

Why? If you have a type 4 motor from the bus just rebuild that.  You can stroke it and add a large bore and have a lot more power and everything will bolt up.

I agree, but the customer doesn't want to pay me for a rebuild, he wants 

something to plug in. The reason I was asking about the 914 swap, is 

a friend of my mine has a good motor in his garage, it's just a long block

and he will give it to me for not a lot of money.

there are several kinds of blocks - each with different dipstick locations, breathers, etc.  do you have a picture of the longblock?

source: i'm running a built T4 in my speedster as well as my westy and have an extra longblock.  i've built several - they are not rocket science.

also - about the flywheel size - generally - the early T4's had smaller flywheels (210mm, then 215mm.  when they mated to the larger 091 trans - they swapped to a 228mm flywheel / clutch).  the 210 and 215 flywheel will work in a VW T1 IRS trans / starter with minor mods. (you need to machine in a small needle bearing).  using a 228 - you need the matching starter.