tire confusion

[cuzncletus]

I'm building another Hodaka trials bike from parts. My first bike is on a Wombat frame and is running an 80/100x21 front and a 120/100 rear with no problems. This new bike is a Wombat motor in an early Ace frame with a modified Dirt Squirt swing arm. I had a new 2.75X21 front tire so I ordered the same brand 4.00x18" rear. Both of these tires (Maxxis) appear quite a bit wider compared to an older unmounted 4.00x18 Pirelli rear and a Cheng Shin 80/100 front. The tire size charts say they're comparable sizes but they sure don't look like it.

Will these Maxxis tires mount on stock Hodaka rims and does anyone have any experience with a 4.00X18 clearing the swing arm?

[mac]

You probably already know this,but the Squirt swing arm is an inch shorter than the Wombat arm so that could create clearance troubles. Also,not all 4.00 tires are the same exact width so the Maxxis could be one of those that,s a bit wider.
What all was involved with getting the Squirt swing arm to fit the Ace frame ? Sounds like a good mod.