?? Sorry to hear you are getting away from the Onan, they're very good engines and its likely all that is wrong with the Onan is that the intake manifold needs to be resealed. It's likely that the manifold is leaking air, the engine is running lean and needs lots of choke to get started. Wish I knew where you lived as I might be interested in buying the onan.
There was one version of the 60xx's that used a honda, I am not sure what model. Without your tractors serial number I really don't have much to go on.. I know the last 6020's built around 2000 did not use Lovejoy brand couplings, but a different brand. If is a Lovejoy, it should have a coupling model like L-110, L-090 and based on that 'coupling size' you can look up what model number has the correct bore to match your crank. Product Catalogs - Lovejoy - a Timken company
There was one version of the 60xx's that used a honda, I am not sure what model. Without your tractors serial number I really don't have much to go on.. I know the last 6020's built around 2000 did not use Lovejoy brand couplings, but a different brand. If is a Lovejoy, it should have a coupling model like L-110, L-090 and based on that 'coupling size' you can look up what model number has the correct bore to match your crank. Product Catalogs - Lovejoy - a Timken company