I'm surprised it's that early a model. I had assumed it was a later model than my friends old one. His had the boiler in the cab near your left knee. Certainly kept you warm.
Is your one still a large chain drive to the back axle?
Sentinel continued to sell steam powered wagons into the 1950's I believe, so even though you say the engine was poor, compared with a Gardener diesel, there must have been something about them.
Once you've got the pioneer restored you'll be able to do a back to back 1930's road test.