Sorry for the delay replying, trying to sort out piles of things this week, so struggling to get any Blatchat browsing time.
It's no bother scaling it up in reality. The way I do it is take the longest "good" dimension (Between points that are pretty secure/fixed) I can get from the sump or block, and scale the plan to be the same. That gives you a fixed line to work the rest from if you need to move any centres.
I printed out a copy and draped it over the sump and it looks to be bang on. I'll put it on tracing paper for a more thorough check before beginning to fabricate, but I think I've revilla's generosity and effort to thank for saving me a fair bit of time with the callipers.
Plan is to check with the tracing paper, then design in CAD a pattern which I can get laser cut, fold up and weld to make the sump. It's for a dry sump, so some complication to it, but it'll give me something to play with for a while 😬