Can anyone help me with regard to the correct manufacturer and part number for a muffler/exhaust on a 1968 S engine.

I have seen both Bischoff and Leistritz, were they both used during 1968 and if so what determined what was used with what.....was it no more than which supplier's exhaust was in the factory? Is there any difference in quality between the two? Were there any other manufacturers in '68?

In terms of part number the catalogue quotes 901.111.011.08 for the 911 T, L and S......I have seen some with later part numbers such as .10 and .11, how do these differ and/or are they equally suitable, why the changed part number?

Plenty of questions, any help appreciated.

Regards
Tim