SCPU and its 128K Fast Static RAM, 512K ROM and use - how?

Hi!

Longer time I never searching this area, but current requirements needs to explain me few things about my own SuperCPU128.

128K Fast Static RAM
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It replaces standard Commodore 64 (64K) and Commodore 128 (128K) operational RAM.
In case of C64, only one half and second half is used as form of OSROM (Operating System ROM).
Ok, this is written about SCPU64 in C64 - but how is it in case of C128 - where is place for OSROM?
Also here's Q - 128K FSRAM replaces operational RAM - is possible to access replaced RAM - looks like unused, but it can be also mirror of FSRAM, but this is unclear - knows anybody anything more?

ROM
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128K uses C64, contains OS overlays - which are downloaded :) to OSRAM - ok, again what in case of C128?
SCPU can accept up to 512K ROM - how and have anybody template for using it? For example to create ML monitor supporting X65 (8502 etc), 65K (65816) and X80 (Z80) CPUs...

Or is here Q: 2nd half of FSRAM is used same way like in C64, and RAM1 of C128 is used true not replaced? It looks logic.
So, finally:
FSRAM replaces operational RAM - is operational RAM free to use? If, how?
ROM -512K how to create own in any template? To today I finished not CRT or BIN C64 cartridge for VICE x64 'cause Forum64 boys helped not... so this I mean for this problem. I know how to create ROM for internal/external socket, also C128 cartridges, but template for C64 works not, so can anybody help?

Thank you for all.
Miro