Hot Rods 1932 roadster "cowl shake" ...what causes it and how do I fix it?

I have finally gotten my 32 roadster on the road, and after about 40 shake down miles, I cant help but notice that the cowl of the car seems to kind of shimmy back and fourth at any bump in the road. what causes this, and how do I go about fixing it?

Brookville body with bolted in dash, aftermarket boxed chassis, dropped beam axle in front, steel brookville floor bolted in, split down the middle for the trans. I have not aligned the car yet, and it seems to have too much toe-in by eyeball, so I guess that is the first step? I braced the body behind the seat, and foreword to the door latches in the rear 1/4 panels before paint, but I didn't do anything to the cowl besides a bolt in brace from the steering column mount at the bottom of the dash, foreword to the firewall. It's an original firewall, installed the stock 32 way with the rubber gasket. If it matters, I'm running steel wheels with Coker bias-look radials 6.7-15 and 8.20-15

 

See if you can find someone who has the equipment & still knows how to spin balance wheels on the car. Well balanced front wheels helps with cowl shake.
Also, unsprung weight is a factor. On a lightweight car, you want to keep the unsprung weight to a minimum. the lighter the wheels & brakes the better.
If you are running Early Ford brakes, and are using the new replacement drums, they are much heavier that original Ford drums. That's a problem on lightweight cars. I stay away from the new drums for that reason.

 

Weld a roof on it?

 

It has Willwood disk brakes on all 4 corners, and vintiques 15x5 and 15x6 steel wheels.