How well do they all actually handle? I assume much better than a MGB GT?
The low powered cars an infinitely chuckable but are no match for a modern car. With my 1300 light understeer was the order of the day with the occasional 4 wheel drift as the 155/80s tried to find grip, body roll is hilarious by modern standards but seems to have little effect on the car's ability to stay on the road, the Dolly forum said that things get scary long before they get dangerous, I'd agree. With a healthy, stock 1300 motor spirited driving involves finding a narrow and windy road and keeping the accelerator pinned to the floor while never actually getting above 50mph, all the power lives at the top end so 3rd gear at 4,000rpm+ and speed conservation are your friends.
The 1850 is another beast. Much more torque at the low end, wheel spin starts can be achieved without even trying in wet conditions. The PO really used to fling it about but I was too chicken, used mine as a comfortable, economical cruiser. To be fair I fucked the steering by coming off a roundabout backwards after owning it a week, they're probably better when the steering doesn't feature 2+ inches of play... I was painfully aware of the fact that if the arse stepped out I'd never be able to catch it, although the Dolomite steering is usually very tight and accurate, great road feel, as evidenced by the 1300.
Having said that it was still great to take advantage of the torque, sat at 60 in top gear and stamping the go pedal would get you to terrifying speeds in a satisfyingly loud and rapid manner.
The 1850 isn't really all that fragile, there are two main problems. Water pumps start failing are are a pain to replace, this also causes overheating which is the downfall of the Triumph slant-4. If you cook a head gasket taking the head off can be an utter nightmare as the studs really enjoy snapping, it's do-able but I opted for buying a whole spare engine rather than ever try and take mine apart! The second thing is the timing chain, a good chain and tensioner will last about 60k, however a lot of cars are fitted with a Rolon chain/tensioner kit which are famously made of chocolate and can and will fail within a couple of thousand miles...
The 1300 lump is the same as the Spitfire/Herald unit (mostly), all the parts are available and it's insultingly easy to work on. The only thing to watch for is ensuring it's getting good oil flow and that the bottom end isn't rumbling, rebuilds tend to occur at about 100k or so depending on use. They are also low geared, 60mph in top is damn near 4000rpm, but you'll never know 'cause there is no rev counter!
The 1500 is a 50mph plodder, use the torque to keep the revs low and they'll last just fine. Extended use higher up the rev range causes the big end bearings to vanish at an alarming rate, and overdrive gearbox helps a lot.