The transom should be strong enough as long as you use say four attachment points (similar to the
Pearson boarding ladders quite often fitted to the 323), then use backing plates/large washers (min) on the inside/outside, again using the ladder (if you have one as a guide),for the plates some thing like Minimum 2" -3" diameter,this is only 20 Hp you are talking about with very limited torgue on that small prop, moving the Pearson wont be easy at first as they are a quite heavy style vessel,and again stopping power will be basically nil if moving forward at any pace, as it's a sailboat I'm sure you would rather be sailing and this temporary fit up would be there for no wing or helping on /off berthing!
As previous remarks it must be done correctly how ever i dis agree on the amount of work to do this- i could knock this out in a morning, but could not re fit a different
engine probably in much under a week, Fitting a different engine has a host of things to establish:
1) Engine room size
2) Engine
bed height and room under sump/width of engine
bed
3) Length of new engine compared to previous(prepare to move mounts)
4) Height of engine compared to previous
5)
Gear box to fit or not(perhaps comes with
gear box?)
6) Gear Box ratio's are they the same?
7) Engine mounts move or
refit or resize
8) Engine alignment to shaft(to be with in a few thou)
9) Gear box flange (is it the same to fit
propeller coupling?)
9 a)
Fuel lines/fittings/possible re run
10)
Wiring panel to fit
11) Extract old
wiring loom and replace with new
12)
Exhaust connections/ alignment/re size issues
13)
Water intake size and location /re run hoses/correct size for new engine
14)
Battery cables and
alternator cables (re -run or change)
15) Throttle and gear boxes linkages and adjustments
16) Engine trials/ sea trials
And countless other minor or major annoyances that WILL crop up, whether it's a 2- 3- 4- 6 - 8-12-16 cylinder all these above items need to be taken into account and after spending thirty plus years as a
commercial Chief
Engineer i can tell you to do it "right" takes time, way more than fitting an out board bracket!!
Cheers Steve