HP110+ upgrade DOS2.11 to DOS6

[time27]

Hi

My resources
1. 2off HP47511 or HP110 Portable Plus

2. copy of DOS 3 to 7 version which I wish to install

3 ROM Burner - GQ-4X4 USB Universal 40 pin Programmer

4. I have M27C256B-12F1 - ST Microelectronics EPROM

Would love to do

Burn a upgraded copy of a DOS2.11 to DOS 5 or 6

What I have done so far:

I have taken out existing HP110+ software draw ROMs and read them.
First few lines of which is HP product number...

What I failed to find is a location of DOS2.11, I think it is soldered to the main board.
Did you guys ever upgrade the DOS??
I did try to load DOS3 by setting CONFIG.SYS to bypass PAM,
by using
> SHELL=A:\COMMAND.COM /P A:\
I used the HP9114B to load DOS3 into A: and I rebooted - I hope.
HP110+ hung, had to use battery reset...

What do you think of my approach?
Did you have a different approach?
https://photos.app.goo.gl/y5DYptc35sFsCvZK8

Regards Nick