My company is a small aerospace supplier that is in negotiations with
an OEM customer.  We produce an assembly comprised mostly of purchased
detail parts.  The OEM used to supply the material to us on a
consignment basis, so they know the exact cost.  Now they want us to
buy all of the parts and manage the inventory in addition to
performing the assembly operation.  We are negotiating the allowable
mark-up on the cost of the purchased parts to cover purchasing,
material handling and interest costs associated with managing the
inventory.

I am looking for an AUTHORITATIVE source that can substantiate the
customary mark-up on purchased parts for an assembly in the aerospace
industry, specifically.  Ideally I would like a survey or other
aggregated data from a respected source or journal such as Supply
Management.

Generous tip promised for a timely response with clear, persuasive,
and most importantly, authoritative results.

Watch out

You will find that they also want you to 'buy' their existing inventory from them.

The next thing you know you will be 'buying' their purchasing
department, their warehouses and all sorts of crud that 'might be
useful'.

Finance will be on tap.

Just tell them 'we don't do logistics'
- walk away 
- you know there are pitfalls - or you would not have asked the question

Tactfully, you could say: 'that is not our skill set'

It is one thing performing a defined process and occassionally
'helping the client out' and rather different when you take over
and/or inherit the stuff that you are not set up to deal with.

Stay clear - they are selling you a poison pill.
If you succumb to the temptation - then set up a parallel operation
that cannot damage your core company.
- Just a comment