Found a cheap RD400 for sale locally. Very cheap. Has Bassini chambers, some brand of rearsets I've never seen, and a nice Yamaha sculpted seat.
Missing a few odds and ends, but its mostly complete. The headlight is too small to be a RD400 light, and someone ground off the fender mounts off the fork sliders. And the carbs aren't stock. I'll have to pop them off to see if they're larger than the stock 28mm, but it doesn't look like it.
And I got the Alfa to turn over today!