Overhauling the engine gives an ideal opportunity to check out the transmission. Check all the major components for wear or even damage while you have the 'window' available. It would be a colossal waste of time and effort to carry out a successful rebuild of the engine only to suffer a noisy, or unreliable gearbox after reassembly.
If some parts are found to be worn or damaged then this component and possibly some of those listed below, perhaps also parts interfacing with the damaged item, may end up in your shopping cart?
Try and renew both the damaged and worn item along with the part it interfaces with to save premature wear of the new part.
Add as many items as you wish to the same shopping cart, new bolts, seals and gaskets for example, and still only pay the same single fixed price shipping cost.
Try this pro-workshop gasket sealant: 08CRAHLG120G for more professional results.