Good questions Dexter..
1.) Yes. A company called Autech did some S13 Silvia conversions for the Japanese market in 1988-1990 I beleive. It is believed to be only a production run of 603 vehicles.
We have a couple owners of real JDM silvia 'verts on NICO. Covert is in Japan... he owns one... Also jdms13rhd is from Alberta, CA... he owns 2 of them... one for sale if you are interested.
Thread showing Covert's car as well as Allens car.. .
zerothread?id=109152
2.) The Infinity M30 is the closest Inf. ever came to the S13 chassis... It's not quite the same... Someone else may chime in with more specifics, but I would guess it's closer to the old Maxima chassis that an S13.
Per http://www.autoconsumerguide.com**********************************************************1990-92 Infiniti M30: Highlights
Complementing the new Q45 "flagship" sedan from Nissan's luxury division was the entry-level M30 coupe, also introduced for 1990. Essentially an Americanized version of the Nissan Leopard, sold in the Japanese market, the M30 was intended as a temporary stopgap, until a brand-new model could be developed. Dimensions were close to the front-drive Nissan Maxima sedan, but the M30 had rear-wheel drive and weighed about 300 pounds more. Maxima provided the 3.0 liter overhead-cam V6 engine, rated at 162 horsepower; but it was mounted longitudinally in the M30, rather than transversely. A 4-speed automatic was the sole transmission. Antilock brakes and a driver's airbag were standard. "Sonar Suspension II," also borrowed from the Maxima, used an ultrasonic sensor mounted beneath the radiator to "read" the road surfaces and adjust shock absorber damping accordingly. A cockpit switch let the driver choose soft, medium, or firm damping mode. Like the bigger Q45, the M30 was marketed as a "one-price" model, fully equipped with only two dealer-installed options available: a cellular phone and a CD player/changer. Standard equipment included a power moonroof, automatic climate control, leather upholstery, power windows and door locks, a 2-way power driver's seat, limited-slip differential, 4-speaker Nissan/Bose audio system, and antitheft alarm.
Year-to-Year Changes1991 Infiniti M30: An M30 convertible joined the original coupe this year. Convertibles were transformed from coupes by American Sunroof Corporation in California. A standard power top automatically latched/unlatched at the windshield header and also raised/lowered windows at the same time.*********************************************************