Hello, Ben,
I have NetBSD 4 installed on an Intel 486, and it works well. I recall about 5 years ago trying to install 6.1.4 on it as well, but I don't think I was even able to boot. I'll try a newer version and see what happens. I see you have 32MB of memory, which I have run 7 generic on before (different CPU though).
Is yours an 80486SX or DX? That's one issue. I've seen dmesgs from true 80486 systems (the 486DLC is a 486-class CPU made to work in an 80386 socket), like so:
https://dmesgd.nycbug.org/index.cgi?do=view&id=5832I expect you'd need more than 16 megs just to boot, considering the size of a GENERIC kernel. Paired down, 16 megs should be plenty. I'm running NetBSD 9.2 on an m68030 system with just 10 megs :)
Thanks, John