While I will agree doing conversions are fun, I will disagree on the statements that have been made here regarding cost and viability of conversions -VS- "airplane" engines. CH Ignitions cost at least $50.00 less than stated. Bought 6 of them now for my conversions. Why buy all the parts for a Poulan? You can buy the whole saw for less than that at times brand new, sell the leftovers. Heck I got 30 bucks for the bar and chain! Paid $70 dollars for the whole saw from sears. Poulan makes Craftsman. Sure the Poulan 42 may be a tad heavier than my true BME 50 but in my sons Sig Extra 300 it has unlimited verticle. Total cost breakdown: Saw $70, hub and sensor bracket $39.00, muffler $28.00 all welded, CH Ignition $145 with Bosch cap. Grand total of $282.00. Less than half of the cost of a so called airplane engine. Remember that BME singles are right out of the Echo chainsaw line. Have a BME 50 in my Wildhare Extra 300LX. Had to invest $650 or so in it. Just started 2 new projects based on the Echo short blocks. CS4400 = BME 44 and a CS510 = BME 50. Paid $350 for both short blocks. Hubs, mufflers, and ignitions will cost me another $250 or so to buy, but I am making everything but the ignitions. Carbs are all over RCU and Ebay for way less than one may think. Get some G10 board for the carb spacer, a 2" by 2' bar will make blocks for at least 20 engines. Paid 22 bucks for mine. By the way BME uses a single prop shaft. Never had an issue with mine. Just my experience.