I imagine you've seen the other Lancaster plan at outerzone.uk also. I'd probably take either one of the plans and use them for the former outlines, drawing keels from the plan and building it somewhat like a Guillows buildm with simple keel and former construction. Really simplifies the build, versus trying to figure out exactly what the designer had in mind, especially when there are no build photos for many of these vintage plans. No chance of talking you out of foam and using balsa? With 1/32" sheet there are a few dips and waves, but they can really be lightened up from using 1/16" or heavier sheet. I've been using it for fuses all the way up to the size of the Comet build, keeping the weight down with good results.
If you want a really good Merlin engine sound, you can't beat gearboxes, although they're obviously more effort to mount and fit than outrunners. I like the mini-Merlin sound I got out of my P51, with a geared 370 inrunner setup: