I was going to suggest upgrading to a big block 460 ford engine.That would be pushing that outdrive. I would make some upgrades to your existing 351 Windsor engine. i would leave the bottom end alone but do a compression check on all the cylinders first and make sure thet are to spec.Then i would remove the cylinder heads,cam shaft,intake manifold and carburetor.Decide if you want to upgrade the cylinder heads from cast iron to aluminum. If you stick with the cast iron heads have a valve job done on them and put a good set of valve springs on them.Next pic a good cam shaft for this engine check and see if a hydraulic roller is available for it, something with adv. dur. of 260 and lift 440 this size cam will give you good power and a stable idle so you can still shift your outdrive without hurting it.Find a good aftermarket exhaust something like imco or eddie marine.Dont be shy upgrade the single roller timing chain set up to a double roller style.Also replace the old stock cast iron intake manifold with a good duel plane aluminum type.I'm sure since the engine is a ford and omc it probably came with a holley 4bbl. carburetor.That is a good carburetor but you will have to rejet it for all these upgrades.Install a good size k/n marine approved air cleaner.Almost forgot your engine probably has a points ignition.Upgrade that to an electronic type.Pertronix makes a kit to upgrade your existing distributor.After this is all done you will also need to upgrade your propeller to a good stainless steel. Find a prop shop in your area and they will probably have several you can test and purchase.This should put you in your budget and give you some extra horsepower.

The gm engine is fantastic! You will run into some problems with installing it.The bell housing,engine coupler,front engine mounts,and exhaust is not compatible from the ford to the gm engine. You will get more horse power from the set up i told you about then the gm vortech and will run into a lot less problems with the install.