Hi woody294, I've re-read the thread/posts and feel that your dad's original 'gut' feelings were much closer to the original design of this boat than he realised and worth re-consideration.
The Sea Queen and Huntsman kits have near identical 'Vee' hulls and both kits were intended for the marinised i.c. aero engine/single prop propulsion of this earlier era and now sold, many years later, largely unchanged as 'classic' model kits. The S.Q. kit is a modern re-manufacture which has been 'slightly' modified for a single electric motor. This clip is a build with a glow plug .61 i.c./single prop:
http://www.youtube.com/watch?v=oqBLIpfdbKUThe Huntsman kit is a popular 'evergreen' design based on the famous Fairey offshore boat which achieved fame and some success in 'offshore' competition at Cowes for some years. The Sea Queen hull is a near identical design to the Huntsman and both models share 'vices and virtues' inherent to both the Fairey hull form and the limitations of these elderly single prop kit designs.
The original boat/hull was designed for twin shaft/props/rudders.These kit designs were adapted to suit the only power source available to modellers at the time to get these large/heavy 4 footers planing. This expediency added a second layer of problems and issues which aggravated the stability and handling of this hull form which modellers experienced, especially in turns etc. when planing.
Be guided and inspired by the original............. You and dad can adapt the kit and 'personalise' 'your' boat......... get the hacksaw out and modify/adapt the existing and return it correctly to twin everything as the original designer intended............ it's a lot more fun and offers the challenge your dad was interested in taking up for enjoying. You are a team with more than enough skillsets to research/modify and build it.............. it's your cash/effort and enthusiasm which is at stake.
All the equipment apart from the shafts and riudders you buy for SQ will easily transfer to other large/planing boats of similar size you may wish to build in the future .......... MTB/MGB, RNLI etc. or use/swop the gear to power a pair of single proppers when the mood takes you. Buy multi-channel rc gear (minimum 3/4 channel) and you can use it for any of your builds. Unless you want to fit a bow thruster, then a mixer is unnecessary and a lot less fun than 'twin stick/throttle' or 'tank steering' on 3 channel with independant matched esc's which gives all the handling options of independant control on both props that the original craft enjoyed.
(I entirely agree with Peter on the points he's raised re. the single brushless route.)