No prob, happy to help
If you are undecided on which engine, just be aware that using an MT75 box will mean you have a slightly smaller drivers footwell, & the pedal box needs to be made to suit the available footwell space
, its not a problem, just needs to be thought about early in the build.
For the corner braces, just a small length of steel approx 6 inches or so with angles cut to fit will help brace the engine bay.
Best wishes for your build
cheers
andy