What engine should I use?

I was given both of these models quite a while back.  
They both seem to be in pretty reasonable condition, and the fellow who gave them to me said that he had taught his kids to fly on them many years before.  He is now involved in SAM and flies Old Time R/C these days.  He seemed a little vague, but thought that he'd scratch-built them from plans from Hearns Hobbies, one of the largest and longest surviving hobby shops in Melbourne AU. I'd say they were built late 60s or 70s. He couldn't recall what engines had been fitted.
The one on the right has tissue covering and the one on the left has plastic film.  There were a couple of punctures in the tissue which I have patched, one just near the leadout.  
The red film is quite good.  It uses tissue for the sides of the turtledeck and the tissue covered one uses mylar? (we used to call it celluloid).  Figure that out??  Both have red tissue covering the vertical stab.  You may notice the red one has an extra rib in the inboard wing, making it about 2" longer.

The tissue covered one measures 24" span & the other 26".  A 7" chord gives them 140 sq" & 160 sq" respectively.  Weight is 170 grams & 190 grams. That's 6oz & 6.7oz.   They look to have home made aluminium bellcranks, with soldered fixtures.

The tissue covered one is probably a little fragile to fly but I would still like to install a period-correct engine as it displays nicely.  The other one I might try to fly, so need to choose an engine which will suit the size & weight.  I have sat a couple of engines in the noses but all seem to make them nose heavy, so I need something light.  The tissue one I had thought a Cub .099 may look about right, but still seems too heavy.  That's not an issue with this one, but the other will need to balance right.  I can't think of an engine that will suit for the size of the plane and the lightness required.  The bearers are quite wide and something like a Cub .074 or even a Tee Dee .051 are too narrow.  The mounting screws are right back close to the firewall already, so I can't mount rearwards.  A Gilbert (I'll get one in the air one day ) has to mount well forward due to the rear induction.  I have a number of Enya .09s available but they're pretty heavy & probably have more power than needed.
Happy to hear your thoughts on engine choice.

Rod.