G1 Serial # location on engine is this accurate

[lakebuggy]

2 Questions: First Project need support! Thank you ....

We have a G1 1981 Serial# located on the frame under the bumper side J10-031111 can only be used for parts.

1.) We have another G1- unable to locate serial number on frame like the other has...(looked same place as other) Can it be anywhere else.
Found Serial # J31-151461 on the engine, does this mean it is definitely a 1987 or did they use this engine for several years on a G1. Any where else we should look to confirm or can we move forward with this as the year?

2.) Can we use 1981 parts for a 1987 G1 before we create a nightmare by mixing the parts?

1st Golf Cart ever