If you joined this forum eleven years ago then you would probably have picked up on the vibes surrounding supercharging these cars. There is nothing stopping you fitting a supercharger but as Colin says there really is only one option for mapping the ECU and that is Chris Flanagan at Retro Sports Cars who is well known on this forum.
The TB replacement will give you a possible increase in bhp but only by about 15, taking it to 275.
Nich.