I think every M42/44 owner has dreamt of an S42 replica at some stage. It's either that or a Downing Atlanta Supercharger but options are equally illusive.
Probably why most people with a 318is in search of more power look for an extra two cylinders.
Hartge also made stroker versions of the engines, 2.1 & 2.3 litre with complete engines and also kits comprising the crankshaft and conrods and pistons as far as I recall.
I've been watching a set on German ebay for the past year off and on but for the cost you could probably buy two E36s