Dan, My goal has always been to put on size. HOwever, I have a few obstacles:
1. My genetics, I am clearly a hard gainer (long tendon attachments, etc.)
2. Most of my life I have been involved in endurance type sports (so my fibers are probably "pre-established to be slow twitch)
3. I have had some good results with creatine, however, other supplements (i.e., Meal replacement shakes, etc.) many times cause me to have G.I. disturbances
4. I still feel the need to maintain good C.V. health due to family history of heart disease. Any thoughts that can help me put on lean muscle mass (I am 35 y/o, 5'7 and 148 lb.)

You have put some thought into your situation! It is difficult to develop size if you are also performing a larger amount of cardiovascular exercise. With your family history it is a good idea to maintain a good level of cardio fitness. However, there is a difference between cardiovascular training for performance vs. health. When you start doing cardio for 40-60 minutes 4-5 times per week at a higher intensity level (75-80% APMHR) you start moving into the performance category. On the other hand, great cardio health can be maintained with 20-30 minutes of aerobic exercise at 65-70% and 3-4 times per week. Many of the top experts in the cardio field would echo this same statement. Remember, there is a difference between performance and health when it comes to cardio exercise!

With this in mind, try moving into a 4 Day Strength and Power Program or the 5 Day Bodybuilding Mass Program. These programs will provide all of the physical stimuli you will ever need for getting big!

Also, try eating every 2 hours. I know this can be a major pain but many naturally "thin" people respond to a more consistent nutrient and calorie intake throughout the day. This may also keep you away from some of the G.I. distress you mentioned. Some of those meal replacement shakes can really fill the old stomach up and drinking a whole one down in one sitting can be tough. Try using only half the mixture and then add in a tablespoon of Flax oil or Udo's oil (see recommended readings for Udo's oil). Fat provides a phenomenal caloric source and as long as it's from a quality, unsaturated product. These positive fatty acids are also good for the heart!

From here it's all just consistent hard work. Let me know how it goes!