All the Matra's are mid engined 4's:
Jet/DJet
M530
Bagheera
Murena
Also don't forget the DeTomaso Vallelunga, Ariel Atom, Opel Speester, Renault Sport Spider, Ginetta G2,3,4,15,21,23,24,26,28,30,31,32,33, Lancia 037, S4, ECV1 and ECV2.
The porsche cayman and BMW M1's are 6s.
Apologies - not all of the Ginetta's were mid engined. I don't know enough about the various models to say which but the most produced (the G15) certainly is.