Hello there,
If you have a Marshall footswitch with the 2 switches, its really easy to get someone that knows what theyre doing to change the jack input to a dual RCA connector, i just got the tech to mark exactly what switch does ( i.e Red/Yellow ) what on the pedal and the back of the amp, they work exactly the same for a fraction of what you'll pay for a vintage one. I have exactly the same amp as you and have done this with the afforementioned footswitch. Ill post you a pic in a little while. You probably already know but the distortion channel sounds amazing, epecially with a distortion pedal in front of it and the reverb is fantastic also, only slight problem is the reverb is quite noisy, as in i get wuite a lot of background humm when i use it, not the distortion though.