I'm having problems with my 66 fuel pump and I thought I would change it to the 67/68 style which is still readily available and hopefully less problematic. I was wondering if anyone has a photo of the bracket that is used to mount the fuel pump in 67 or 68. I can't find a part number on marineengine.com to see what it looks like.
This "modern" fuel pump would work on your motor, since it has a hose-barb-style vacuum connection (same as your 100hp's existing fuel pump), vice the other commonly-used-style fuel pump which mounts to the block (and corresponding vacuum port) with 2 screws.
You should be able to easily modify your existing fuel pump mounting bracket to locate the new pump.
There are tons of these available fairly cheap on eBay, just do a search for P/N 0438559.
Look for a good used OE pump (there's one on there for $14.99 shipped!), or new OE part, US-Built. There are a lot of cheap Chinese knockoffs out there and I have no experience with them to testify whether they are reliable or not.