Even the little A10 engine could handle a B20 ute, with two adult passengers, a tank full of fuel & a 1/4 ton payload, so surely an A12 can handle a stripped down buggymobile.

Give the thing a proper tune up, check that the advance systems in the distributor work properly & stick a vacuum gauge on it.
At 700rpm idle it should run smoothly & pull about 19" hg of vacuum at sea level. A little less at altitude.
If the vacuum readings are seriously down, then you have a problem.