On a car that age it will only be as reliable as the maintenance that was done on it.
chances are you have a 302 engine and a c4 trans both made ford famous but yes if proper maintenance was done it will be a great old car i have a 73 torino likr the one clint had in the movie but with a 351w and is a fun old car
If it's a '77 Country squire it has either a 400 which was standard equipment or the bigger 460 which was optional. The 302 was not available on that car. Both of which are/where good engines if taken care of properly. Regular oil changes and routine maintenance like changing filters, PVC valve, plugs,dist.cap and rotor,etc. and it should last a long long time. The Dura-Spark ignition that Ford had in those years was very reliable also. Other things to watch for are suspension items like idler arm, tie-rod ends and ball joints that will go bad after 100K miles or so . That car will have a C-6 transmission , not a C-4 and the C-6 is basically bulletproof and will last forever and if for some reason it doesn't, they are fairly cheap to rebuild compared to an AOD or similar tranny with overdrive. All and all, if you can live with the 12-14 mpg gas mileage, then you got a fairly reliable car so hang on to it as long as you can. If it's got a good body on it , with little or no rust, they are becoming quite collectable now with baby-boomers from that era. Kenny.
Looking for a Used Country Squire in your area?
CarGurus has 6 nationwide Country Squire listings and the tools to find you a great deal.