Terry, not sure of details but don't a lot of folks end up with wider tires simply to run close to stock rolling circumferance with more readily available modern tire profiles like 60 or 70? I think this is the issue Dan is bringing forward. 78 or 80 profile tires are difficult to source our side of the pond, but this may be less of an issue in Europe.
I would recommend trying the car without major resto work on the engine, clutch, and transmission to limit the present work scope. Pulling the engine/transmission unit with the body installed is not a complete show stopper, and realistically adds at best two weekends to the time required. Taking on the re-build at the same time as the frame / body / suspension restoration is a big undertaking and can be very stressful IMHO.
I did all the work as one project, but I contracted the engine re-build, MT75 & clutch details, and prop shaft to a specialist as I did not have the required skills. This approach worked very well as the major drivetrain components were off site during the DIY frame build and the work was done to a high standard. The drawback was the additional cost, a lot of time spent sourcing engine parts during other work, and having to transport the engine transmission to the shop and back home for installation in the frame prior to marrying the body. I also had to transport the finished car with drivetrain installed to the specialist for MOT inspection and starting / comissioning of the engine, as the specialist (quite reasonably) wanted to do the initial start-up in case there were any problems, who is at fault, damaged reputation should there be an issue, etc. The engine & transmission ended up out of the car after assembly anyway due to miss-assembly of the clutch components, and it may be coming out again this winter as this stuff is still 'not right'.
As I take it you would prefer to do most of the work yourself, keeping the drivetrain work as 'desert' and a separate project has a lot of merit. It also improves the odds of you ending up with a completed running car rather than a for sale stalled project in boxes. No one ever sets out to create one of these, and unfortunately they are all to common in the hobby. I must admit there were days I thought I was close to this outcome with the car's components all scattered about.
Thankfully my BTDT friend was able to settle me down so I could perservere to completion. Gordon Lund's book has excellent advise regarding being realistic about the DIY work scope and selecting parts to contract out.
If you are skilled enough and keen on the DIY engine rebuild, just make it a separate project after you have a running (or at least assembled) car. Of course, if you want to fix the obvious on the engine like water pump, carb service, oil leaks, etc., not a big deal. I am thinking here more of a total rebuild with machining, oversize pistons, head work, etc. Question, have you at least confirmed or intending to confirm the car starts prior to taking it to bits?