Hi Will,
IMHO an 1850 would make a very good road rally car. It'll never be as competitive as a top-spec Welsh Escort, but will be an awful lot cheaper to build!
I'm a road rally navigator, so I've sat in all sorts of things

For a RR build, you're looking for reliability above all else - you can't go stupidly fast as you're on the public highway after all. The Dolly has proper twin-wishbones at the front, and 4-linked rear, although the standard brakes are a bit weak - TrackerJack on here sells a conversion using Sierra calipers and Golf discs which makes them a lot better. The slant-4 is a nice torquey lump, and at a rough guess I'd say the 1850 is slightly slower out of the box than a 1.6 205 - A stock Sprint would be similar to a Golf GTI 16v. The Sprint is one of the very few 16v cars that can be road rallied on carbs, as it is a single cam (the road rally rules only allow cars with more than one camshaft per bank if they are fitted with the original injection system...)
Like all cars, the shell would warrant strengthening if you're intending to do rough events, and the lights could do with upgrading (6" KC daylighter lenses drop straight into the 5 3/4" housings on a twin-light Dolly)
You don't mention whereabouts in the country you are or what type of events you intend to do? If it's historic, the brake mods etc won't be allowed, there were period brake mods for the Sprint, but the bits are hard and expensive to find now...)
HTH,
Nick