PedroM gives "ROM call unavailable" (it doesn't say which one, though)

Probably ROM_CALL_3CF, which I dubbed "EM_ArchiveMemoryBeginning". I left this name instead of the official one given by Scott Noveck in http://tichessteamhq.yuku.com/topic/2385 , since the official name of this ROM_CALL comes from TI's private header file.

If ROM_CALL_3CF being unimplemented is the only thing that prevents your program from running on PedroM (i.e. that the archive format of PedroM is 100% compatible with that of AMS 2.xx), that ROM_CALL can be easily implemented in PedroM. Assuming the archive memory starts at the nearest sector boundary following the end of the OS, the value it returns should be something like
(((ROM_BASE + 0x12000 + __ld_program_size + <several dozens of bytes for the certificate fields>) + 0x10000) & ~0xFFFF)