My Form 1065 includes a Form 8283 with vehicle donation box checked.  I also attached a PDF file in the EF screen 4 using the default to main form.  (the only link to form option for 8283 was appraiser which isn't true in this case).  I checked the box Form 8453-PE and will mail in the donee organization letter which has equivalent information to the 1098-C.  Lacerte error reject code is F8283-032-02 and F8283-028-01.  Resolution mentions binary attachment which I think means the PDF which I did attach.