A big part of torque loss is from the longer leads between the starter and the battery. Also lead acid batteries have higher internal resistance than the Lithium. The Hobbico should be close in power to the Sullivan. I have the Saito HC 150 on my Rascal 110 right now and the larger Sullivan spins it easily in direct drive, without reduction. If you like , I can ship it to you to try out! The 180 I have actually starts real well with a thick leather glove (insurance) and a back flip. More often than not, first flip from a proper prime.
I know you would have no problem making the conversion, but if you have any questions, The flat pack adapter shown earlier is probably the best way to go. I can help out if you have questions.. Might be easier if I just passed along my phone number .