What's wrong with the aftermarket pipes available? I think some are 1 1/2".
That's the right size, but since the engine is over to the left side (1"? from std. so its sprocket taper lines up with the BT clutch drum) the pipes will fit the engine, but may run into frame and transmission parts.
Both cylinder's exhaust ports point away from the engine and down, but at different angles. IMHO it will require some fabbing to get a compound curve that clears everything, then runs horizontal to the rear. Open exhaust is of course the easiest, 2 mufflers will make it more difficult. Making then chroming will be $$$.
A pair of cross member bars will give you mounts for controls, the easiest attachment is the motor mount holes with longer bolts. However, the bar should go under the mounts to avoid raising the engine. Do you need both front and rear? IDK.
The stock BT foot shift bracket must mount where it has a clear run for the shifter shaft back to the transmission lid.
Here's a 45 frame in silhouette. Note the height difference between front & rear mounts - yours are the same.