It is possible to fit the Luscombe with the same Hanlon Wilson mufflers as the Cessna 150.
Also now that you have the 0-200 installed, and you have probably done it anyway, have you changed the Lord Mounts on the engine? With the larger, more flexible 0-200 mounts, the standard Luscombe engine mount becomes too flexible.
We have one here with the same installation and spacers were machined to fit inside the O-200 mounting lugs and then you can use the 65-85 rubber cones. As you are on the UK permit system this should present no problems if you should do it.
Regards.