To swap SR-20DET into Miata, a complete parts kit is available for bolting SR-20 from Nissan S13, S14, S15 and 5 speed gearbox from S13, S14 directly into Miata with NO cutting of subframe, bonnet or steering rack position.
The site has details, prices and photos of kit bolted to SR engine / gearbox to show quality of work.
The kit includes engine mountings (using the Miata rubber mounts in standard position to bolt to the SR-20) and gearbox adapter that bolts directly to Nissan gearbox to connect to the Mazda Power-Plant Frame (ppf). Gearbox fits into Miata body with clearance and shifter fits in original position.
A fully fabricated sump is available that is a direct bolt-on replacement that has integral oil passageway and pick-up, includes a stainless steel pressed oil separator tray - full length of engine and all hardware. Sump is level with lower edge of subframe (fully protected and no loss of ground clearance) and allows engine to fit under standard bonnet. Sump has been extensively tested in motor-sport application.
Kit takes away all the hard work of installation whilst keeping engine, gearbox and Miata suspension, steering standard for ease of replacement parts etc. Kit has been available since 2004.