Too slow for motorways?

[Dogstoat]

I am travelling back to Plymouth from Roscoff tomorrow. Destination Warwick.
The M5 north has some long, steep climbs on the way and my old 1990 non-turbo and very heavy Foster and Day Chuggabug can struggle.
At times, I can end up in 2nd (sometimes 1st) gear to get to the top of some long inclines.
At what point do I become an unacceptable hazard?
It does concern me…..any views?

 

[Minxy]

K & N air filter that are steel mesh construction and will allow a better flow of air into the engine

We used something like that for our Reliant Robin van, it really did make a difference.

 

[jezport]

With it being an old non ECU vehicle, with the right person who specialises in old mercs I bet you could do a decent engine swap? I would start researching, as long as its rust free