RE: Magnum 80
I built 2 of the Magnum 80's back shortly after article came out. Then 2 more a few years later.
Originally I had 2x K&B 40's. At the time twins were not cool and not at all popular. Being deeply involved with drag racing at the time I flew these like I would run the Funnycars...flat out
It took a while and one plane to get comfortable with the twin as a daily flyer. We had a very short runway by todays standards so brakes were necessary. Not much was available so I made my own. Servos were expensive for the radio I had. There were Rohm retracts on both planes as well as the later ones. I used A/C freon to operate them. It was dirt cheap then. I made my own fuel as I had ready access to nitro,alcohol and Klotz oil. It was not uncommon to hit the field with 18 glow plugs, several gallons of fuel, dozen props and a flight box full or misc stuff. Sometimes I would leave the field owing props and glow plugs to everyone. I was an environmental disaster everyday. haha
I blew up the original motors pretty quickly as the planes were very fast and the motors unloaded a lot in the air. I had 2 speeds...full throttle and idle.....usually one motor out landing. the second generation motors were K&B 40 with fuel pumps. these ran terribly together. I occasionally used up a gallon or more fuel and never got in the air fooling with them. I made it even worse adding tuned pipes from my Dirty Birdy 40's.
The 3 gen motors were K&B 6.5 rear ex with tuned pipes and fuel pumps similar to the article. It took a while to get them running well but when they ran they were awsome. The cops recorded 125+ mph many times. Their radar seemed to miss after about 125 and would just not read. Eventually I added more nitro and the motors really got with the program. I finally blew a rod right out the side of one and the other had a cracked piston. I repaired them and ran them untill the head bolts stripped out.
Later I built another pair and flew them for a couple more years before one crashed in a cloud of pieces and I retired the last one.
There was a later version of this plane that I never built. Somewhere I still have plan for both. haven't seen them for years.
If I was to do it again I'd probably put some modern 60's on it and longer gear legs, brakes would be nice. A separate flap arrangement would slow tha landing down a bit. Todays radios are much lighter so you can cut the weight down some. I liked the fully sheeted versions much better. The vibrations quickly destroyed the first wing. I replaced both wings with foam core and fully sheeted. Much better. The last 2 were built up but fully sheeted. One layer of 3/4 oz cloth, one coat of thin primer, sand and one more coat of thin primer, one coat of thin paint. that was it.
I have ony one surviving picture somewhere. I'll try and dig it out.
Good luck on your build. These are great flying planes with reliable motors.