If I'm not mistaken, you may be able to use a block & piston assy from 170400 or 190400 engine models. ....I think your crankshaft journals & rear cover will fit those blocks and connecting rods.
What is the model & type of your engine? ....I remember them as being model 143302, but some paperwork says differently.
Are your engine numbers on a flat plate attached to the cooling fins?
Is that flywheel puller a B&S tool ? ...I never saw, or used, one like that.
ID tag sits on the flat plate PTO side of the cooling fins.
This engine is a 142301 -502075 Serial 239253
The puller is a B&S one , I think it shows it in their parts lists