You're right about the oil lines. On some models of the marine 427 the oil lines loop right up in the way and the oil filter is on top of the port side of the motor, on other models it is located farther aft.
In any case, changing a fuel pump on a 427 is a bugger of a job. I just looked at one of my spares sitting in the shop, and I don't know how much room you have on the forward side of your motor, but on my 38 there is precious little room. You may actually be able to shore up the motor and remove or rotate the forward port side motor mount out of the way, and gain access to the pump there. In any case, under the best of situations, this is still going to be a tough job. I'm not a big fan of electric fuel pumps, but I think you can see why some people have decided to convert to them. I have a set of new fuel pumps, but have not had occasion to install them yet, and if luck holds out, perhaps I never will.
If ("if") removal of the front motor mount (and perhaps the front motor mount assembly too, which also holds the final fuel filter gives you enough room to get an extended socket into the two securing bolts, it will still be a tight fit. I would be tempted to try that route because removing the exhaust manifold is STILL no assurance you'll have any better access. Take a close look at your particular installation, hopefully you have a lot more room in your 42 than I have in my 38.
The photos above show the potential access route if you can secure the motor, jack it up a bit and remove or rotate the motor mount out of the way. Since I have not done this job personally, I'll defer to those who have. Having recently reinstalled a transmission oil cooler with similar hard copper connections, those will also be a bugger to get back aligned and threads properly started.
Good luck, hope this gives you a viable alternative and prompts some addl comments.
Regards, Paul