The midsection extension kits are made by
http://www.baymfg.com/, cheaper than buying a new leg but still very expensive.
Trying to lower a motor by using a jack plate generally doesnt work, cables etc will foul the transom as will the steering cylinder if you have hydraulic steering.
Below is a reply to an inquiry I made with Bay MFG regarding a kit for a 225 hp Mercury:
Thank you for your interest in our products. I have attached our 613 parts sheet for your review. All parts are included that you will need. The spacer is already painted. Current retail price is $880.00. We can ship direct to you or you can go through a Mercury dealer in your area. We have shipped to many dealers in the UK. Picton Boats, EP Barras, 4 Ocean LTD, Bargain Boats, Adrian Cronk Marine, Bembridge Outboards, Trio Moulding Marine, Ribcraft, Riviera Boats, Sea & Shore, West Coast Marine, Professional Powerboats, Bursledon Outboards, Outboard Motor Specialist, Dave Crawford Marine, DB Marine, DK Fiberglass and Mobile Marine Engineers. Maybe one of these would be close to your area. Let me know if you have any other questions.
Cheryl Kirk/Sales Dept.