Touring cassette...

[Spokesmann]

Ive got a 42/49 on the front here with a 34 on the back, added a Shimano Tourney to help with the shifting:

 

[Spokesmann]

My 73 Continental with 36 on the back (6-speed screw on block) with 42/53 up front, copes with just about everything.

 

[contadino]

The vendor advertised it as a GT, and the photo shows a GT cage, so maybe it's this model which just shows "SunTour Cyclone" on the body but GT on the cage?
If so, it can handle at least a 32t and probably a 34t cog.
If you're going to fiddle about with the chainrings you'll need a new crankset; a modern 34/50 compact with 110mm bcd would be easiest way to go, but an old Stronglight with 86mm BCD would be more in keeping with the bike's vintage. These obsolete cranksets and chainrings are now scarce, though!
The FD, assuming it's the Suntour cyclone shown in the advert, is certainly capable of a wide jump between chainring sizes.

Flippin' heck! You must have eagle eyes. Yes, it does say GT on the cage. Just been out to check.

So, I'm going to be buying a new wheelset in the next few weeks. I can just get a 'megarange' block on it and swap the wheels based on the terrain. I guess it would just involve tweaking the limit screws.

That would be Ace.

Thanks so much for that. Much appreciated.

 

[stevevw]

You will need a new chain too. Bigger cog, long mech arm etc.
I have just bought a Crane GS to make Eroica a bit easier this year. this also takes a 34

 

[contadino]

I bought a new wheelset and got a new block with a megarange on it as discussed and it turned up last week.

Here it is, albeit with the old chain on. The new chain is an extra link in length. The old one got up onto the big cog fine but the shop sent the chain of a certain length so I figured that maybe they know best. Works like a charm. I've only been out for a test run and the two hills weren't much of a challenge beforehand but I crawled up them on the new granny gear just to try it out.

So a big thanks to @Poacher for saving me some dosh and helping me keep my shinny stuff.

 

[bigjim]

My 73 Continental with 36 on the back (6-speed screw on block) with 42/53 up front, copes with just about everything.

Do you ride with that Brooks saddle at that angle?