I'm on Windows 7 x64 and have a 5:4 monitor (1280x1024) , and selected the 4:3 aspect ratio. I learned that the game internally renders to 1024x768, which is then put out at 1280x1024 to my screen. Everything is really small that way, incl. the hud.

I tried to force 640x460 via windows compatibility modes, but that only seems to have effect on the internal rendering. On the screnn everything is the same size, just more pixelated. :-(

Is there a way to decrease the view port, and/or increase the hud size?
Thanks in advance!

To get bigger HUD in this game, you must lower the resolution. Unfortunately, you can only select aspect ratio in modernized version, and you get 1024x768 with 4:3.
Of course, another option is to buy a bigger monitor.

First you can look at the table I made:
https://ibb.co/h4rkdo
Green are the most suitable resolutions for given screen size, orange acceptable and red unacceptable.
Monitor resolutions are in brackets, as they are not important if you have scaling enabled, they are just the most common resolutions for given size.
I measured the HUD height in upper left corner, where John's watch is.
In my opinion, perfect height is between 52 and 63 mm. 50mm is too small and 65mm is quite big.

Now you can also measure the HUD height on your screen.

You didn't say which size the monitor is, but if it's 17", then it's really small, same as if I play on 1680x945 on my 27", but I rather play on 1600x900.
If that is really so, then unfortunately, you have the worst monitor (I certainly hope nobody has 15" these days) for this modernized version.

Also one thing, you actually don't need a HUD in this game, as you are quicker with hot keys. But it's true that when the HUD becomes too small, everything else becomes too small and it puts a lot of strain on the eyes.

Your best option would be to install the old version, download dgVoodoo 2 and play on 800x600.
Second option would be to contact the guy on WSGF who made exe's with different resolutions. Now it only contains 1280x1024 and all widescreen resolutions from 1280 to 2560. But I already posted on forum if he can provide instructions how to HEX edit the exe, and he didn't respond.

Thanks for your long posting. My monitor size is 19''.
Yeah, I guess only the old version would do the trick, or a large monitor. ;-)