personally, I'd use an L16 or L18. Still carbed so easy to engineer. Conversion itself is not too difficult. Can be done with the standard manual transmission tunnel if you pay attention to what you're doing. Either L16 with L18 crank or L18 with L16 rods. Mill standard pistons to flat tops at around zero deck height and choose your own CR, a works 76 cam grind and twin 40s. Made 116rwbhp in my old coupe. You'd be well and truly in the low 14s.
Plus you get strong cheap 5spds with the L series conversion. An A series running 14s will blow gearboxes regularly.