i would get rid of that motor, it's too big, too heavy. a small frame motor is the way to go. It just won't "feel" right with that large frame motor. Also the torque converter may not line up, not sure about that. personally i would use an HS50 but an HS40 would be Ok too. it appears you live in snowblower territory, it shouldn't be hard to find an old snowblower with an HS50.
also get the black paint off the rear chrome shock springs, that looks weird. you can take the sebec shocks apart and put on new springs. i do this all the time for a fresh chrome look. i would do the headlight and chrome fenders in a chrome color too. on the front brake i would adapt a db30 disc brake caliper to the fork stay. i do that all the time and it works quite well, because finding the original front disc caliper is difficult and expensive (db30 caliper is $15.) a duck tail seat is hard to find. newer non-ducktail seats you can get off ebay, but they don't look right, and the snaps don't line up with the snap holes in the frame.
personally i would add the head gusset to the frame too. you have a 1971 model, and it's before speedway added the head gusset. with adults it's easy to crack the head plates without that gusset. i do this to all 1971 models, it really stiffens the frame and prevents that crack from forming (if it's not already started to crack!)
done right, the scarab/scorpion speedway is one of the best 10" wheel mini bikes ever made. it's worth it to get it dialed in. i buy new chinese series20 torque converter drive/driven with a 3/4" belt. and set the gearing up right (usually 11t jackshaft sprocket), and this thing will really surprise you. BlackwidowMS is getting ready to sell new speedway torque converter covers, so you'll be all set there.
