What were your tires originally??
Yanmar originally had a rear tire 12.4/11 x 28 on the YM336d, but they changed the YM336d tire size
about half way through the model run to 13.6 x 26 Firestones. Of course this also meant that they had to change the internal gear ratios front to back...which they did.
I have the notes for our YM336d which was the later model.
The original OEM rears on our YM336 were Firestone (BridgeStone) All Traction Field & Road R1 6 ply.
13.6 x 26 6 ply tire mounted on a 12 x 26 rim*
Front to Back internal gearing was 1.694:1
The unloaded height of that tire is 49.5"
The rolling circumference (RC) Tire spec is 147" supporting 2760 lbs load @ 22 psi
Rolling circumference will vary with the load.
Measured RC on our tractor with a loader and back blade I got 147" to 148.5".
That was done with a series of averages on hard pack and pavement both 2wd & 4wd.
The problem was that Firestone doesn't make that old tire anymore. They make a tire that measures the same diameter and RC, but it is made to measure that on a modern 14.6 x 24 rim. So that would need a different wheel... ugh! Maybe someone else makes a tire to fit your rim that is the right height & RC.
The original OEM fronts on our YM336D were OHTSU 8 x 16 4ply R1 ag. mounted on a 16x6 UA rim*
*note that rim width for tractor tires was originally measured on the INSIDE faces of the rim where the tire contacts the rim.
you should check with each wheel or tire manufacturer to see how they measure width because automotive tires are measured differently for width.
rScotty