new rear derailleur for old school 80s road bike.

[30yroldclunker]

So 80s era road bike. I recently changed both 8 speed rear cassette (now 11-32) and added a smaller front chainring (now 38-52). My derailleur is Shimano 105 from that era, I have down tube friction shifters. The derailleur is a short cage (SS in Shimano terms) and I want to change to a medium cge (GS) to accomodate the new drivetrain capacity.
Would a modern 105 like this
https://www.wiggle.co.uk/shimano-105-r7000-11-speed-rear-derailleur/
which is rated for 11 speed cause problems with my set up bearing in mind my cassette is 8 speed and chain is a HG40
https://www.wiggle.co.uk/shimano-hg40-6-78-speed-chain/
or would it be safer to go for the 9 speed rated Sora derailleur?
https://www.wiggle.co.uk/shimano-sora-r3000-9-speed-rear-derailleur/
I guess what I'm trying to work out is whether the new 11 speed rated derailleur cage is narrower than my original cage and would cause issues.

 

[carlosfandangus]

Just checked mine, the new 105 has a 10 mm cage, so does the Sora one!

 

[si_c]

Should be fine if you are using friction shifting, make sure you get the GS rather than SS derailleur. The alternative would be to search ebay for a Shimano long cage derailleur that is period correct - something line an 300lx derailleur should work fine.

 

[30yroldclunker]

excellent, thanks for the replies.