Pearson 10M's with the Volvo MD11C were equipped with a Walter v-drive reduction gear (2:1). The engine is mounted with the shaft exiting forward and the v-drive redirects it aft under the engine to the shaft log. The Walter Maching Co. is still available for technical support and has rebuild kits for the v-drive.
The Walter Maching Co. Inc.
84 Cambridge Ave.
Jersey City, NJ
V-Drive Installation on Volvo MD11C (1978)
Farymann Diesel U.S.A.
870 Route 530
Whiting, N.J. 08759
I don't know much about the A4 but there are several sites with a lot of information. It would be silly for me to try and duplicate these excellent web rosources here so follow the links below.
Atomic 4 Info Sites
Ron Davis'A4 info page ... This is the place I would start...
Atomic Four Engine Service co. ... Great info and an excellent history of the A4
C&C Photo Album Site ... The excellent C&C Photo Album web site has PDF versions of the A4 owners manual and A4 service manual.
Moyer Marine ... Don Moyer is the world reknown A4 guru
Several 10M's have been re-powered over the years. Engines installed have included Universal, Westerbeke, Perkins and Yanmar. Barry Meehan (#168) wrote an article on the process of changing from an A4 to a Westerbeke in the Pearson Current Volume 4, #4 1998. The article can be found on the NPYOA website but you need to be a member for access.
I made a table comparing engines from several manufacturers. Most of the content is from Joe DeMers. Joe is a Beta Marine dealer and I think he was able to supply more complete information for the Beta engine in the table.
Engine Comparison Table
The engines in the table are in the 25-29 HP range. That may be more than needed in the 10M. Some additional research is needed.