Cold series 3

First off, i'm a newby to this site - so Hiya! - got an old 1976 series 3 'Rag top' that i'm using to run in and out of work and slowly sorting out it's many problems.
i hesitate to ask this - cos i know it's an age old Landy problem, as i don't want pages of ridicule! (deep breath), Once i've got the damn thing started(Glow plugs?) the temp gauge never really goes above the "cold" white block. (Unless i rev the 'tits'off 'er going up hill!) I think its the thermostat which i want to replace ( just to give 'er indoors some semblance of heat when she's in the landy - and my ears a rest!) - but the manual (Haynes) talks about 2 different types of thermo' - so how do i know which ones on mine? - I see plenty of thermo's for sale on ebay rated at 74 deg. - would this be ok?
oh, and any problems i might encounter? - like studs liable to snap etc?

Hello, and welcome. (there is an introduction bit, called introduce yaself)

They generally don't run that hot, unless they're working hard, but you normally get some heat from the heater. I'd guess the thermostat is stuck open, or missing, or the wrong temp. 74deg is about right for initial opening.