Termux, SimH, VAX780 emulator, OpenVMS 7.2 takes about 5.4 Gb for all of it. The tricky bits were getting gcc to work and compile SimH. I imported a set of virtual system disks that I had already installed OpenVMS 7.2 on to from my desktop machine. The huge obstacle there is getting a system license key. There are key generators in the wild.
I can telnet in to the virtual VAX from my other PCs.
One caution, updating Termux removes all your data. I lost a VAX that way once. 8(
I run an 11/780 emulated system on my phone on days I feel nostalgic.