Just looked into this thread, nice job!

My advice would be if the 90 engine will fit in the cowl go ahead & use it.

With a smaller lighter engine you may end up stuiffing useless lead in the nose to get the balance right so if the bigger engine fits just use that. You will be able to spin a bigger propeller & the engine will be just chugging along & sounding much more scale like than a smaller engine running flat out. Plus you will have a bit of extra power when you need it.

I have a DH 60 Moth at 1.5 me span with an Enya 80 four stroke (twice the size recommended) and the combination is ideal. I use Sig Koverall on fabric covered models & I'm very happy with it. - John.