Hi Dave,
This is a great thread!
I too have this kit (unbuilt) and although it has its faults, I personally think it's a fantastic production!
If you wanted to build your SE5a with a full engine, rather than the partial representation of the Wolseley Viper, as supplied in the kit, and were willing to make the necessary alterations/changes, "Model Art by Marco" produce an exquisite and complete 1/8th scale model kit of the Hispano Suiza engine - the other powerplant used in the SE5a.
If you're up for it here's a link for you: http://www.modelartbymarco.com/
I bought one myself in preparation for my build and I can highly recommend it. It contains over 60 cast resin parts and detailed step-by-step instructions. A photo of the finished item is available on the website.
Just a thought...
Cheers and good luck!
Derek