Went to Lowes and Home Depot and checked online. Lowes has the Troybilt TB575EC 29cc 4cycle straight shaft trimmer for $199 and the Jumpstart is $47. The trimmer (none on display) appears to be like ant 2cycle in size. The Jumpstart is basically a battery, switch, gear drive and the output shaft is a hex drive (allen wrench) so would be easily duplicated with available materials. They also have a 4cycle leaf blower which is 25cc (model TB4HB) and is $170. The Troybilt web site wasn't very helpful.
Home Depot hasRyobi and have displayed two 4cycle machines: a RY 34440 (S340) straight shaft 30cc trimmer for $199 and a RY34420 (C430) curved shaft 30cc trimmer for $174. The weight and feel of these are indistinguishable from 2cycle machines IMO. Ryobi sells refurbished machines online. The 34440 is listed at $150 (plus shipping) and the cheaper curved shaft 34420 is $130. Since both are 30cc and just the engine would be used the cheaper one makes sense. Both have good reviews.
Here are th links:
After looking ove the Ryobi trimmers I don't see any problem with stripping them down and adapting them for marine use like any other brand of 2cycle as we've done in the past. I'm going to check several local dealers to see if they have any returns kicking around and to get some input as to how they compare to the 2cycle versions. It's looking good so far.