Frame

[RDFL]

https://www.ebay.com/itm/1977-Yamaha-RD400-Frame-Straight-clean-ca-title-custom-mono-shock-race/184464267079?

[IR8D8R]

From the rearsets I would say drag bike. No other reason for prone riding position. The whole thing looks distorted but I'm not used to looking at bare 400 frames. What's with the headlight mount? Fairing?

But then why would you do a mono shock on a drag bike?

IR8D8R

[bitzz]

There's a headlight, a bunch of dash lights and a horn.
Says street bike to me

[RDFL]

Fairing mount strapped to head and has mid top and bottom too, agree with streetbike. Would like to see pic of it in its heyday, just a guess but would suspect hasn't been on road since mid to late 80's.

[m in sc]

its a cobbled up 400 frame for a streetbike for sure.  look at the frame rail on the LH side on the rear, holy cow hacked.

the rearsets are akc or dg. very good actually, old school ones.  But having used them before, they are good.

looks like an lc arm?  that thing is a fucking mess.