Regarding mods, the eTug deserves mention.
A Pawnee with a 350 cubic inch Chevy LS1 running on Mogas. Early experiments provided too steep a climb angle, so the original 4-blade prop was adjusted to decrease the climb rate. Now it has a different prop.
I've hooked many gliders up to eTug, yet to tow behind it.

https://www.glidingclub.org.au/membe...aircraft/etug/

These days a crate LS3 engine can be purchased for about $8000 and produces 430HP on Mogas. Car engines require a PSRU (speed reduction).

https://www.gmperformancemotor.com/p... AhPlEALw_wcB

Not much concern about shock cooling or leaded Avgas going away.
Jim