Question

[chumbucket]

Good thing you beat MJ to the punch there AJ.
Manifolds and risers are a fairly easy job that most anyone with basic mechanical ability can tackle.
Water pump kit in the lower unit isn't particularly difficult either but you've already got a mechanic working on that.
The hardest part on both jobs is getting the mounting bolts out. On a car engine, manifold bolts remove easily because they are subjected to constant heat. Boat motors don't (or at least shouldn't) reach the same temperatures. Still, I've never had too much difficulty getting the bolts out. Use some good marine grade anti-sieze when re-installing. ;)