Well it may not be a thunderbird but its definitely bird engineering!
Nope,
definitely NOT!
All Birds with a slanted engine are mono rails
(one tube from the steering stem to the engine)
That one clearly is NOT!
In fact all three share the same frame (the spoker, the nighthawk as well as the thunderbird)
with only very minor differences (tooling is expensive you know)
That means all differences I pointed out above remain true for all Bird engineering mini bikes that look anywhere near OPs bike.
So yeah, go ahead and find me the Bird engineering Ad with that frame depicted...
I'll start in the opposite direction:
Frankly that engine mount looks alot like
FOX/Dynamark to me
Also Fox is known to have used spoked wheels in the seventieies...
and the Banshee 125 is very very close IMHO
(but earlier models also had a single down tube)

Sooo I'm not totally against pointing in that direction.
Some other mfgs used very similar engine mounts (cat, speedway etc..)
Oh talking of which... Speedway -uhm- ... shrike?
isn't too far off either
But I'd stick with
Fox tbh
mainly because THIS is a banshee 125 (as in the ad)

And this is (unfortunately the smallest imaginable picture)
what I call a banshee tank on a bike frame exactly like yours (wink wink):
ebay auction for the one above said:
1970s FOX Banshee 125 Mini Bike Motor Cycle
AMERICAN MADE
Rupp Era
GOOD PROJECT BIKE
This auction is for a barn fresh Fox Banshee 125. A restoration was started many years ago but did but get past the dismantling. You are buying a good parts bike restoration project. I believe the motor is the original 3.5 HP
Tecumsah engine. The tag has been removed. The engine turns over and has good compression and should start right up. The frame is in nice shape with no welds, looks like original paint. I have the break and throttle cables.
This bike is staged for the photos, the motor seat and gas tank are not attached to the frame and just were put in place for the photos.
I do not have the chain or the mounting bolts for the engine or gas tank.
The chrome wheels are are in nice shape and should clean up nicely.
Tires hold air. These Fox Banshees do not turn up that often and this would be a rewarding restoration project.
Please contact me if you have any questions.
This bike can be picked up in New Milford CT 06776
Sorry no shipping and I cannot provide shipping quotes.
You can get an online quote from PLYCON
'sid
PS Budget.. your turn... Bird me wrong
PPS oh it could've been much easier
https://oldminibikes.com/forum/index.php?threads/mini-bike.161633/
second post showing a two rail Banshee... *sigh*