I have a 2 ton engine tag M35  80180 trans tag tractor No 70483.manufactured by Holt Stockton.
The exhaust manifold is different to any 2 ton's I have seen and has a Shelbar Marvel carb. No provision for the exhaust pre cleaner arrangement and the chimney goes straight up through a hole hacked in the bonnet.
on the other side of the engine there is no oil line from the head down to the side of the block
Anyone able to enlighten me what i have, thanks for looking WF

I have not seen that manifold before. My guess is it was for trying to burn heavier fuels in the 2-Ton engine.  I like the looks of it. The Schebler has been added by someone as a replacement carb. The parts book lists the Zenith T5T carburetor starting at serial number 70439. The oil return tube from the cylinder head to the crankcase was not used until 74322.

A keen observer will see a bolt beside the engine tag top photo. I am thinking that has been an attemt to fit a dipstick rather than fool with level plugs.

Cool tractor. Being a 70xxx serial number, you have a Peoria built Holt tractor (1925). When production moved to IL, the name “2 ton” was adopted.        The correct carb should be a t5t although a model 63 zenith should work as well. I picked one up on eBay for cheap with a whole rebuild kit. Very neat tractor. 

Thank you for posting the serial reference. I have a 2-Ton here which I believe is closer to 1926, than 1925, which sort of bums me out. I purchased it for restoration to honor my mother, who will officially turn 100 in May 2025. Kind of an odd way for me to remember my own mother, but some tractors here follow my families birth dates. JM