Richard,

I think your '73 US Bus was originally equipped with a Type 4 1.7 engine.
There is a 17mm lenght-difference in the transaxle's primary shaft between
the trans used with the upright engine and the one used with the Type 4 engine.

Since post '71 1600 Busses were never exported to the US you'll have a problem
locating the front and rear bresttins that will fit the '73 Bus/1600 combination.
You can't use the '71 tins cause the enginecompartment changed around august '71.
(not sure it's the correct date)

Another thing your '73 doesn't have is the airfilter bracket on the right in
the enginecompartment, welded to the right-rear fenderwell.

The rear enginemount of an original '73 1600 is different from the '71.
I think (not sure) this is also a non US part. The holes in the chassismembers
will match both this "late" 1600 rearmount and Type 4 rearmount.

Hope it helps,

Brian.
'73 singlecab
Holland