That kit looks very similar to the one I got from vegaspaddy, which he bought at a garage sale. Who did you get it from, please?
As for the ride characteristics, you've described a fairly typical Delta trike experience. The biggest source of the scary feel to the ride is the height of the seating position as compared to the CG of the trike. If you fab up a seat mount that brings the seat down on top of the rear triangle, effectively making it a crank forward vehicle, it will help some. Of course, that will require different handle bars, but that is easily arranged.
Tadpole recumbent or semi-recumbent tikes are more stable. Also, a lowrider cruiser frame with a delta trike conversion and crank forward might work better.
Are those 24 inchwheels? If so, where did you purchase them, please?
By the way, that's a nice looking job you did there. I hope my current project looks half as good when done. I have a Huffy 24 inch ladies bike I am converting, and putting the HT engine in the rear triangle. Seat is moving back about 6 inches, and as low as I can get it - I'll basiclly have the engine between my thighs.
) so far using that design and all of them needed bracing 
