You are aware that Coveland in upstate NY
makes a miata based seven kit for a very reasonable price. Why order from across the pond when you can buy right here in the good ol USofA. Below is a quote from the Coveland site.
Specifically designed for the Miata drivetrain , and will work with other IRS drivetrains with simple modifications. Designed to need No welding to mount a 1.6 or 1.8 litre Miata. This frame has been specifically dimensioned to properly fit the Miata engine and transmission. The rear differential mounts are located and a double plate used for strength. A plate has been added under the differential giving strength to the frame and the differential. Brackets are already welded to use stock Miata emergency brake, brake lines, and Miata steering column. Other parts used directly from the Miata include wiring harness, guages, Brake calipers, uprights, rack, exhaust header. Upper and lower front and rear wishbones included with the kit. $2,700