Break bridge Silva "flat bottom" is replaced by Silva "arch bottom" from ~ Z6000 (at the end of the production of SLX you can find one of these two). Pro SLX is produced in both versions: SSC with "EM logo" or "narrow without SSC". Confirmed, I accidentally have both.
The history of EM 753 is very mysterious - I described only 1 series, but the frame on reynolds 753 for the people (I do not include teams) was definitely produced until at least 1992 ( the last confirmed frame 753 has the symbol C94xx -1992; by chance I am its owner).
...for most of the time without an official name (Pro 753 was created by analogy to Pro SLX), on the famous photo from the Black / Yellow catalog (1987) it is the only frame without Golden Box Sticker on top tube ... In 1989 catalog appears Grand Prix model - finally 753 has got its model in EM! ... for the entire 2 years

... then 753 is annexed by Corsa Extra model and produced further - unfortunately I do not know until when (after 1990 753 appears only once - as an option Corsa Extra in 1992 catalog). Again, 753 is produced in both versions: "wide" or "narrow". Apparently, the EMC was not covered with chromium frame 753 - indeed, so far I have not been able to see it.