Sorry to break it to you mactjaap, but in addition to 1MB RAM, you are also running 128K ROMs, which for all practical purposes makes this a Mac Plus without SCSI, which could be easily added (and supported by Apple) with a Dove Mac Snap card. It is "technically" an upgraded 512K, but functionally it is a Mac Plus. To advertise it as anything else would be false advertising. I had a 68040 Duo 280c which I upgraded with a Power PC 2300 logic board. So is it still a 280c, or is it now a 2300, despite what the case says? You no longer have a 512K. Period. You are running a base model Plus without SCSI. And the Plus is just not that impressive for this exercise as it has been done many times before. Don't get me wrong, i'ts great to Have any Mac this old operating as a web server from a floppy disk, but No new ground is being broken here.
I've not seen a D.P.S. RAM card before, but there were literally dozens of companies during 1984 through 1986 who were trying to capitalize on unofficial and unsupported RAM upgrades for the 128K & 512K, competing mostly on price and to a lesser extent quality of the upgrades. Yours is most likely a late model card which required 512K base RAM and the 800K drive upgrade kit, to boost it to 1MB to 4MB configurations. Actually fairly common. RAM was expensive in those days so, even a minimal upgrade to the bring it up to the functional equivalent of a base model Mac Plus 1MB was HUGE, and likely the most common. Apple did not even start offering 2MB Plus & SE base configurations until 1988.
As far as your server, the program "requires" 540K to work, and while it may work with 200K, it may also require 128K ROMs, which is REALLY doing more for you than you realize. Also, how are you reducing the available RAM? Are you using a RAM cache? if so, realize the Program may actually be utilizing portions of that cache, or even disk caching to work around your imposed limitations. The fact remains you have 1MB RAM installed. And how much free space is on the disk? And here's another consideration for you: you say you are running 6.0.8 as a maximum, what is the minimal System configuration you have tested it with? The stock 512K will not run any system higher than 4.1 which may also be a limiting factor as well, keeping the base model at a minimum of 512Ke, which was released AFTER the Plus!
But since you brought up System 7, it requires more than 1MB RAM to boot, so even an early stock base model Plus or SE configuration would not boot from a System 7 800K Disk Utility disk.
Bottom line - you really should test this with an actual 512Ke (with only 512K physical RAM) installed before you make the claim you are running a 512Ke server, or at a minimum disclose the upgrade to 1024K RAM.
I've not seen a D.P.S. RAM card before, but there were literally dozens of companies during 1984 through 1986 who were trying to capitalize on unofficial and unsupported RAM upgrades for the 128K & 512K, competing mostly on price and to a lesser extent quality of the upgrades. Yours is most likely a late model card which required 512K base RAM and the 800K drive upgrade kit, to boost it to 1MB to 4MB configurations. Actually fairly common. RAM was expensive in those days so, even a minimal upgrade to the bring it up to the functional equivalent of a base model Mac Plus 1MB was HUGE, and likely the most common. Apple did not even start offering 2MB Plus & SE base configurations until 1988.
As far as your server, the program "requires" 540K to work, and while it may work with 200K, it may also require 128K ROMs, which is REALLY doing more for you than you realize. Also, how are you reducing the available RAM? Are you using a RAM cache? if so, realize the Program may actually be utilizing portions of that cache, or even disk caching to work around your imposed limitations. The fact remains you have 1MB RAM installed. And how much free space is on the disk? And here's another consideration for you: you say you are running 6.0.8 as a maximum, what is the minimal System configuration you have tested it with? The stock 512K will not run any system higher than 4.1 which may also be a limiting factor as well, keeping the base model at a minimum of 512Ke, which was released AFTER the Plus!
But since you brought up System 7, it requires more than 1MB RAM to boot, so even an early stock base model Plus or SE configuration would not boot from a System 7 800K Disk Utility disk.
Bottom line - you really should test this with an actual 512Ke (with only 512K physical RAM) installed before you make the claim you are running a 512Ke server, or at a minimum disclose the upgrade to 1024K RAM.