It depends on the year of the M7. Since roughly 1995 the M7 has a slightly longer wing. The problem is the empty on the M7 is higher.
And yes the m6 without the aileron extension(which they incorporated into the last handful), is truck like.
Check this site out -
Maule AK Worldwide - Home
Autogas is a good reason to go with the 235hp, but not all 235 are the same. I'm not sure which sub models maule has used. There's some that are still 8.5:1 compression but have a 2400rpm red line to limit it to 235. Other's have 7.2:1 pistons and spin at 2525rpm. The latter would be what you want, and they were certified on 80 octane. It's the O-540-B series.
That said lycoming service instruction 1070 shows you can use appropriate auto fuel in the other engines just fine.
https://www.lycoming.com/sites/default/files/SI1070AA Specified Fuels.pdf