70 Barracuda is going to get a new bullet and rear end. The car has not been gutted and won't be a lightweight. What do I need for a driveshaft? What is a good diameter, wall thickness and material to specify? I am not class racing so no need to get exotic. Probably use 1350 joints. What kind of yokes are normally recommended for something like this?

I got mine from Dr Diff(Cass). Its by strange. If I remember correctly its 3.5" steel. I did not upgrade to the billet yoke. Mine uses 1350 ujoints. Been running it in my 4000lb plus wagon for 6 yrs. Not the fastest runs 7.01 in the 1/8th. No issues

I had mine made by a shop that build/repairs ds for heavy trucks. They also build shafts for Pro Stick cars. IIRK it cost about 260.00 with 1350 joints included/ installed.

Strange Engineering will make one for you from premium parts. You can check with a local driveshaft place too and maybe find something made from cheaper materials.
https://www.strangeengineering.net/product/seamless-chrome-moly-drag-racing-driveshaft.html/

I have good luck with Denny’s . They also have lifetime free labor to change the u joints and shorten it if you ever change rear or trans . Can’t beat the nitrous ready shaft he sells . Almost and place that builds you an1350 shaft will sell you a strange or sonnax trans yoke . This is one thing I like overkill on , last thing you want with any car is a broken or twisted shaft beating the bottom of your car !

I have a Mark Williams billet steel 1350 trans slip yoke and a billet 1350 yoke on the rear from Moser. I had a local big truck driveline shop make me a 3" diameter steel driveshaft w/ what they call their "thickwall" tubing which I believe is .090" thick. Also using Spicer 1350 U joints.
It's been fine for a long time, but I don't race nearly as much as I used to. It's made plenty of deep 5 sec 1/8 mile passes, 8 sec 1/4s at nearly 3900 lbs.

Got a few made locally for lower HP cars with no problems. Have used Dennys for the last couple, his prices are reasonable and good quality parts.

just make sure the place you decide to use does high speed balancing.
around here, the local truck garage[s] just do low speed balancing, and at times, this works out. other times, however, vibration issues arise, and i blame it on the balance.
just my opinion. your mileage will vary.

This. I've had shafts made locally that were not quite right. Maybe OK in a street rod or cruiser that rarely sees over 3000RPM. Not so much at 7K.

Strange. Mark Williams, One of the other top shelf shops that do parts for race cars, not dump trucks.

Measure center to center length, approximate trap speed to calculate driveshaft rpm and look at a driveshaft critical speed chart.

I will NEVER use another Strange Driveshaft, I had a driveshaft vibration @ 80mph & above, called them & they ONLY spin them 500 rpm, I got one from Mark Williams & it is now SMOOTH as glass.

I love Strange but not for driveshafts. 20 years ago i was in the market for a new driveshaft for the race car. Its a long shaft. Was going to buy a CM from Strange. Don't remember if it was a 3 or 3 1/2". Was about to buy it and asked what the critical speed was of the shaft. They could not tell me. Called Mark Williams and they said you can't use that shaft. Ended up with a 4" MS shaft from MW and could not be happier. They balanced it somewhere around 7000 rpm.

Bought a 3.5 inch cm from strange with billet ends and billet yokes for a 70 challenger and they made it 0.600 short twice . I had to pay shipping for their mistake . Never again for driveshaft's !

I've had good luck with this local company but have heard mixed reviews in recent years.

https://www.dynotechengineering.com/drive-shaft/drive-shafts

Martin spring and driveshaft right here in Kalamazoo does a great job with driveshafts and high speed balances them too. Very reasonable, never had an issue or hurt one with anything i have had

These bad reviews of Strange backs up what I've thought of them for a long time. I've seen a lot of broken and twisted Strange axles over the years...stuff that shouldn't have broken.

Has anybody used one of the Nascar driveshafts for sale on eBay?

Some are about the right length. 4" diam, 1350 joints, some .065 wall and some .083 wall steel. Made by Dynotech.