jadilla, when I first rebuilt my engine, I was in the same boat (lol). But, never attempted to launch until I installed the after market alternator. I too ran the engine on the trailer, but for a much longer period of time at around 1000-1500rpms. Of course, with muffs and water running. After about an hour and a half, I started to smell unburned fuel vapor coming out of the exaust system, then when I would try and throttle, it would either backfire and or bog with very little power. Also noticed after running this way a few times, the plugs were covered with black carbon. I did this for breakin purposes only and to see if the engine was going to hold together after rebuild being it was the first time I had rebuilt one of the 470's. I am not saying that my battery at that time was up to par but all the same it went flat after about an hour and a half. If you could get a 65 amp marine alternator, you could possibly build a bracket to mount it. But! The problem arises as to allignment issues from the crank pulley to the alternator itself. If you have power steering, then there would be another pulley to figure into the layout. You would have to make sure that the alternator mounting bracket is afixed to the front of the motor securely. You could probably copycat and fabricate but the question arises as to which one you copycat. Dont forget that the block is aluminum. The timing cover is aluminum. There have been posts about guys making there own brackets but shortly after a few months posted about broken timing covers, pulled threads, problems,problems,problems. (mostly home made brackets but not all) Some problems may have been caused by simply a poor design and some because of improper torque at the front of the motor and also misallignment of pulleys causing vibration. Breezeworks 470 talk sells an alternator kit. Talk to Kevin, the moderator. Breezeworks 470 talk is a forum dedicated towards the 470 owners and there are some great people that are willing to help you. Not forgetting this site either! These guys are great too! Whatever you decide to mount up, just make sure you take a straight edge across the front of all pulleys after installation so you are not running crooked with your belt. You will know right away and smell burning rubber if belt is not running true. Your new alternator may also heat up and fail prematurely if not running true. To tell you the truth, I paid $400 for the one I got and it was fabricated (welded) crooked as a dogs leg. The alternator diode did not work when brand new. A buddy helped me fix the diode problem, but the point is: I was totally dissatisfied with the product and actually had to repair a brand new product to make it work correctly. There are several manufacturers but again you will have to determine what is best for you. Just be careful when installing the kit also. Read all of the directions and follow them to a tee. You'll get it, just takes some time,some work, and of course some money! good luck, Tom