I suppose I have nothing new to offer after these fine gentlemen have posted. The Rossi-53 (I love Rossi's) is a bit heavy for the Magnum and would be difficult to shoehorn in there but the Predator, Viper, Sonic (Scat-Cat) can handle the Rossi. Just use some triangle stock behind the firewall and coat the area with thinned out epoxy for a buit of strength and fuel-proofedness (not a word but hey)
It sounds like you have made up your mind but for what it is worth the Rifle (Angel's custom speedster) uses pylon style landing gear and it is shaped similarly to the Magnum and you can choose standard or V-Tail versions. I will be running my West-50 in my Rifle and hope to be underway here shortly.
I dunno why folks care about hand launching an airplane- It is generally pretty easy (after maiden
) to launch them and they are slick with no gear.
Keep us posted Big Bad Guy!