I "really" don't think this will work.

Do I want someone to waste $10,000? Of course not. An RB20 in a Sunny just won't work. The Amount of work required would be huge. The balance would be wrong, the power benefit wouldn't be worth it.

I've even seen RB20 -> S13 Silvia, and they sold the cars soon after.

Asking for an opinion is not asking for encouragement. That's a totally different thing.

I've seen an L28 with triple webers in a 510 at 1999 Shasta. That sounded mean, handled ok, but constantly overheated in traffic. The Firewall had a 1 foot square box section cut into it.

A VG20 is a much better option. Especially if you can get it registered with a turbo.