I approached Mick Allen a few years ago when considering a PA28 "project". While professional and knowledgeable, he scoffed at my plans and questions, making me understand they have so much business, that any non-standard cases slow them down and are unwelcome.
This speaks volumes about their reputation - so much work in spite of a high price - but you may want to be cautious with your "piecemeal" requirement. Just an opinion, will be glad to be proved wrong.
/h88