Hi Manni,
I searched on boat point for a Pelican 27 and came up with "Sara Jane" currently located in Middle Harbour. Is this the yacht you bought for $15,000 or less???
Firstly let me congratulate you on buying a yacht. However keep in mind it is said that the two best days of ownership of any yacht are the day you buy it and the day you sell it.

However if you have bought a "right" yacht, the days in between can be quite enjoyable too.

If you have bought "Sara Jane" or another example of the design in similar condition, I believe you have bought a "right" yacht.

Usually when someone buys a yacht it is for pleasureable purposes and therefore is an emotional decision rather than a commercial decision. Under these circumstances it is common for the "hang the expence" attitude to prevail and more money to be spent than is wise.

All is not lost though as it is still possible to have a ton of fun without breaking the bank or the marriage if you have one.

To your specific question, replacement of the Volvo engine (a notorious propagator of nautical nightmares) and sail drive (which can be just as bad), with an outboard engine.
As a short term and economical solution to the problem, this is a good idea. You will need to get one with a long leg though and you may need to mount it midships on this yacht. An 8hp engine should be more than adequate with a short pitch propellor. This is all fine for harbour river and inshore work.
For coastal passages an outboard engine on a yacht is quite undesireable except for the tender.
Before you committ to a course of action, I strongly recommend you investigate the possibility of fitting say, a Kubota engine to your existing sail drive leg. Hunt around the net and you may be surprised with what turns up. Try these guys first
http://www.diecon.com.au/index.html and
www.marinediesel.com.au/default.asp.There are a lot of other factors involved but I am tired and going to bed. If you want to ask me further questions, message me. Cheers Cisco