I am afraid to start cutting the bottom out of the cowl out of a plane too, but too cheap to buy a Commercial Model gas engine... Here is a pic of a poulan 46cc in a Patty Wagstaff (78") span I think... And a Homelti 25cc on a CG Ultimate (54" span) I am just under the impression it would fit (33cc)... I sat all last night reading up on chainsaw conversions... Don't burst my bubble [&o] haha when you get a chance could you give me rough dimensions of the firewall?? Of a pic of your ST 2500 on it for comparison? I really appreciate it...