If you want to upgrade to 7 digit displays, go with the Weebly MPU board which includes 7 digit support.
The Alltek MPU board does not contain the 7-digit Playboy software nor the hardware conversion for it.

https://nvram.weebly.com/mpu.html

Instructions:
https://nvram.weebly.com/7-digit-display-expansion.html

The 7 digit implementation requires some hardware with a decoder chip to be built. You'll also need to upgrade the Playboy MPU board ROMs with the 7-digit support version. So it depends on how electronically competent you are.
These are already built into the Weebly MPU board.

The other alternative are the 7volution displays which are a plug'n'play solution but they're not cheap and I don't know how well they work with Playboy, and anyway they're all out of stock.

How often will you actually roll over the score on a 1978 Playboy?

I do on mine often enough. Top score is 2.4 million.

I must suck or i have my games set too steep,
I have had 6$ man for 14 years and have only rolled it over once.

Can the high score on the memory be raised to retain a 7 digit score?

With the ROM mods yes it retains all seven digits. The ones digit is always zero so they just shift everything in memory and store the six unique digits.

That is cool!