I'd imagine on these engines the guides are just a cast boss in the head that is drilled and reamed. As others mentioned there are a few different options for guides. Can be done at home if you're willing to buy the proper tools but it'll cost you at least as much in tools as paying a shop, you'll have a learning curve, it'll take longer, and you risk messing it up. For a one off job just find a decent machine shop.
Personally I bring my big engines to a machine shop. My Honda SOHC4 engines I do guides and valve jobs myself. Had trouble finding a shop local that had experience doing bike engines since the shop I used to use closed and this is something I do somewhat regularly. Worth the money in tools to remove and install guides, ream, cut seats, etc. These guides are pressed in though so fairly easy. Knock the carbon off, drive old guide out, port head, new guide in, ream to size, cut seat to appropriate width and depth, lap, etc... Not rocket science but you need to be exact about it for an engine to last and perform well, and some heads are easier to DIY than others.
