We should have the measured drawings for your SR3 but will have to dig a bit. Stamford did supply some custom stuff for Lister at one point (that fit without adapters) but not sure about SR. On top of that, current availability will be an issue. Lister did build adapters to SAE specs for your machine and these will allow coupling to just about any standard modern genhead. Typical cost on a set is now $350 though.
If you would like further details, email me please.
dieselgman